configure: add msgpack required version

configure.ac

@@ -74,7 +74,7 @@ AX_CXX_COMPILE_STDCXX_11([noext],[mandatory])
 PKG_PROG_PKG_CONFIG()
 PKG_CHECK_MODULES([nettle], [nettle >= 2.4])
 PKG_CHECK_MODULES([GNUTLS], [gnutls >= 3.1])
-PKG_CHECK_MODULES([msgpack], [msgpack])
+PKG_CHECK_MODULES([msgpack], [msgpack >= 1.1])
 
 AC_ARG_ENABLE([tools], AS_HELP_STRING([--disable-tools],[Disable tools (CLI DHT node)]),,build_tools=yes)
 AM_CONDITIONAL(ENABLE_TOOLS, test x$build_tools == xyes)