macOS: bump minimum version support

Current minimum macOS supported version is 10.11, but contributions
were build for 10.8. This patch bump minimum version for contribution
to 10.11 as well.

Change-Id: I9d7a45ce2409b309b2bbab5be85b5cbb60801b34

contrib/src/main.mak

@@ -127,7 +127,7 @@ CXX := $(CROSS_COMPILE)clang++
 endif
 
 ifdef HAVE_MACOSX
-MIN_OSX_VERSION=10.8
+MIN_OSX_VERSION=10.11
 CC=xcrun cc
 CXX=xcrun c++
 AR=xcrun ar