Stop support for gcc 4.8, XCode 7.3 and VS 2015

.travis.yml

@@ -78,14 +78,6 @@ matrix:
       env: COMPILER='clang++-6.0'
 
     # 2/ Linux GCC Builds
-    - os: linux
-      compiler: gcc
-      addons:
-        apt:
-         sources: *all_sources
-         packages: ['g++-4.8']
-      env: COMPILER='g++-4.8'
-
     - os: linux
       compiler: gcc
       addons:
@@ -190,11 +182,6 @@ matrix:
       env: COMPILER='g++-8' CPP14=1
 
     # 5/ OSX Clang Builds
-    - os: osx
-      osx_image: xcode7.3
-      compiler: clang
-      env: COMPILER='clang++'
-
     - os: osx
       osx_image: xcode8
       compiler: clang