update dockerfiles

docker/Dockerfile

 FROM aberaud/opendht-deps
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
+
 RUN git clone https://github.com/savoirfairelinux/opendht.git \
 	&& cd opendht && mkdir build && cd build \
-	&& cmake .. -DCMAKE_INSTALL_PREFIX=/usr -DOPENDHT_PYTHON=On -DOPENDHT_LTO=On -DOPENDHT_PROXY_SERVER=On -DOPENDHT_PROXY_CLIENT=On && make -j8 && make install \
+	&& cmake .. -DCMAKE_INSTALL_PREFIX=/usr \
+				-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=On \
+				-DOPENDHT_C=On \
+				-DOPENDHT_PYTHON=On \
+				-DOPENDHT_PROXY_SERVER=On \
+				-DOPENDHT_PROXY_CLIENT=On \
+	&& make -j8 && make install \
 	&& cd ../.. && rm -rf opendht

docker/DockerfileBionic

-FROM docker.pkg.github.com/savoirfairelinux/opendht/opendht-deps-bionic:2.1.3
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+FROM docker.pkg.github.com/savoirfairelinux/opendht/opendht-deps-bionic:latest
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
 
 RUN git clone https://github.com/savoirfairelinux/opendht.git \
 	&& cd opendht && mkdir build && cd build \
 	&& cmake .. -DCMAKE_INSTALL_PREFIX=/usr \
-		-DOPENDHT_PROXY_CLIENT=On \
-		-DOPENDHT_PROXY_SERVER=On \
+				-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=On \
 				-DOPENDHT_C=On \
 				-DOPENDHT_PYTHON=On \
-		-DOPENDHT_LTO=On \
+				-DOPENDHT_PROXY_SERVER=On \
+				-DOPENDHT_PROXY_CLIENT=On \
 	&& make -j8 && make install \
 	&& cd ../.. && rm -rf opendht

docker/DockerfileDeps

 FROM ubuntu:20.04
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
 
 RUN apt-get update && apt-get install -y \
         dialog apt-utils \
@@ -13,13 +13,13 @@ RUN apt-get update && apt-get install -y \
         libncurses5-dev libreadline-dev nettle-dev libcppunit-dev \
         libgnutls28-dev libuv1-dev libjsoncpp-dev libargon2-dev \
         libssl-dev libfmt-dev libhttp-parser-dev libasio-dev libmsgpack-dev \
-    && apt-get clean
+    && apt-get clean && rm -rf /var/lib/apt/lists/* /var/cache/apt/*
 
 RUN echo "*** Downloading RESTinio ***" \
     && mkdir restinio && cd restinio \
-    && wget https://github.com/aberaud/restinio/archive/2224ffedef52cb2b74645d63d871d61dbd0f165e.tar.gz \
-    && ls -l && tar -xzf 2224ffedef52cb2b74645d63d871d61dbd0f165e.tar.gz \
-    && cd restinio-2224ffedef52cb2b74645d63d871d61dbd0f165e/dev \
+    && wget https://github.com/aberaud/restinio/archive/e0a261dd8488246a3cb8bbb3ea781ea5139c3c94.tar.gz \
+    && ls -l && tar -xzf e0a261dd8488246a3cb8bbb3ea781ea5139c3c94.tar.gz \
+    && cd restinio-e0a261dd8488246a3cb8bbb3ea781ea5139c3c94/dev \
     && cmake -DCMAKE_INSTALL_PREFIX=/usr -DRESTINIO_TEST=OFF -DRESTINIO_SAMPLE=OFF \
              -DRESTINIO_INSTALL_SAMPLES=OFF -DRESTINIO_BENCH=OFF -DRESTINIO_INSTALL_BENCHES=OFF \
              -DRESTINIO_FIND_DEPS=ON -DRESTINIO_ALLOW_SOBJECTIZER=Off -DRESTINIO_USE_BOOST_ASIO=none . \

docker/DockerfileDepsBionic

 FROM ubuntu:18.04
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
 
 RUN echo "APT::Acquire::Retries \"3\";" > /etc/apt/apt.conf.d/80-retries
 RUN apt-get update && apt-get install -y \
         apt-transport-https build-essential pkg-config git wget libncurses5-dev libreadline-dev nettle-dev \
         libgnutls28-dev libuv1-dev cython3 python3-dev python3-setuptools libcppunit-dev libjsoncpp-dev \
-        autotools-dev autoconf libfmt-dev libhttp-parser-dev libmsgpack-dev libssl-dev \
-    && apt-get clean
+        autotools-dev autoconf libfmt-dev libhttp-parser-dev libmsgpack-dev libssl-dev python3-pip \
+    && apt-get clean && rm -rf /var/lib/apt/lists/* /var/cache/apt/*
 
-RUN apt-get update && apt-get install -y python3-pip && pip3 install --upgrade cmake
+RUN pip3 install --upgrade cmake
 
 # libasio-dev (1.10) is too old
 RUN echo "** Building a recent version of asio ***" \
@@ -20,9 +20,9 @@ RUN echo "** Building a recent version of asio ***" \
 
 RUN echo "*** Downloading RESTinio ***" \
     && mkdir restinio && cd restinio \
-    && wget https://github.com/aberaud/restinio/archive/8d5d3e8237e0947adb9ba1ffc8281f4ad7cb2a59.tar.gz \
-    && ls -l && tar -xzf 8d5d3e8237e0947adb9ba1ffc8281f4ad7cb2a59.tar.gz \
-    && cd restinio-8d5d3e8237e0947adb9ba1ffc8281f4ad7cb2a59/dev \
+    && wget https://github.com/aberaud/restinio/archive/e0a261dd8488246a3cb8bbb3ea781ea5139c3c94.tar.gz \
+    && ls -l && tar -xzf e0a261dd8488246a3cb8bbb3ea781ea5139c3c94.tar.gz \
+    && cd restinio-e0a261dd8488246a3cb8bbb3ea781ea5139c3c94/dev \
     && cmake -DCMAKE_INSTALL_PREFIX=/usr -DRESTINIO_TEST=OFF -DRESTINIO_SAMPLE=OFF \
              -DRESTINIO_INSTALL_SAMPLES=OFF -DRESTINIO_BENCH=OFF -DRESTINIO_INSTALL_BENCHES=OFF \
              -DRESTINIO_FIND_DEPS=ON -DRESTINIO_ALLOW_SOBJECTIZER=Off -DRESTINIO_USE_BOOST_ASIO=none . \

docker/DockerfileDepsLlvm

 FROM ubuntu:20.04
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
+
 RUN apt-get update && apt-get install -y \
         dialog apt-utils \
     && apt-get clean \
@@ -11,16 +12,17 @@ RUN apt-get update \
        python3-setuptools libcppunit-dev python3-pip \
        autotools-dev autoconf libssl-dev libargon2-dev \
        libfmt-dev libhttp-parser-dev libasio-dev \
-    && apt-get remove -y gcc g++ && apt-get autoremove -y && apt-get clean
+    && apt-get remove -y gcc g++ && apt-get autoremove -y \
+    && apt-get clean && rm -rf /var/lib/apt/lists/* /var/cache/apt/*
 
 ENV CC cc
 ENV CXX c++
 
 RUN echo "*** Downloading RESTinio ***" \
     && mkdir restinio && cd restinio \
-    && wget https://github.com/aberaud/restinio/archive/2224ffedef52cb2b74645d63d871d61dbd0f165e.tar.gz \
-    && ls -l && tar -xzf 2224ffedef52cb2b74645d63d871d61dbd0f165e.tar.gz \
-    && cd restinio-2224ffedef52cb2b74645d63d871d61dbd0f165e/dev \
+    && wget https://github.com/aberaud/restinio/archive/e0a261dd8488246a3cb8bbb3ea781ea5139c3c94.tar.gz \
+    && ls -l && tar -xzf e0a261dd8488246a3cb8bbb3ea781ea5139c3c94.tar.gz \
+    && cd restinio-e0a261dd8488246a3cb8bbb3ea781ea5139c3c94/dev \
     && cmake -DCMAKE_INSTALL_PREFIX=/usr -DRESTINIO_TEST=OFF -DRESTINIO_SAMPLE=OFF \
              -DRESTINIO_INSTALL_SAMPLES=OFF -DRESTINIO_BENCH=OFF -DRESTINIO_INSTALL_BENCHES=OFF \
              -DRESTINIO_FIND_DEPS=ON -DRESTINIO_ALLOW_SOBJECTIZER=Off -DRESTINIO_USE_BOOST_ASIO=none . \

docker/DockerfileLlvm

 FROM aberaud/opendht-deps-llvm
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
+
 RUN git clone https://github.com/savoirfairelinux/opendht.git \
 	&& cd opendht && mkdir build && cd build \
-	&& cmake .. -DCMAKE_INSTALL_PREFIX=/usr -DOPENDHT_PYTHON=On -DOPENDHT_LTO=On -DOPENDHT_PROXY_SERVER=On -DOPENDHT_PROXY_CLIENT=On && make -j8 && make install \
+	&& cmake .. -DCMAKE_INSTALL_PREFIX=/usr \
+				-DCMAKE_INTERPROCEDURAL_OPTIMIZATION=On \
+				-DOPENDHT_C=On \
+				-DOPENDHT_PYTHON=On \
+				-DOPENDHT_PROXY_SERVER=On \
+				-DOPENDHT_PROXY_CLIENT=On \
+	&& make -j8 && make install \
 	&& cd ../.. && rm -rf opendht

docker/DockerfileTravis

 FROM aberaud/opendht-deps-bionic
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
 
 RUN apt-get update && apt-get install -y python3-pip && pip3 install --upgrade cmake
 

docker/DockerfileTravisLlvm

 FROM aberaud/opendht-deps-llvm
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
 
 COPY . /root/opendht
 RUN cd /root/opendht && mkdir build && cd build \

docker/DockerfileTravisProxy

 FROM aberaud/opendht-deps
-MAINTAINER Adrien Béraud <adrien.beraud@savoirfairelinux.com>
+LABEL maintainer="Adrien Béraud <adrien.beraud@savoirfairelinux.com>"
 
 COPY . /root/opendht