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

appveyor.yml

@@ -7,7 +7,6 @@ branches:
 
 os:
   - Visual Studio 2017
-  - Visual Studio 2015
 
 environment:
     matrix:
@@ -34,19 +33,10 @@ environment:
 
 matrix:
     exclude:
-        - os: Visual Studio 2015
-          additional_flags: "/permissive- /std:c++latest"
-
-        - os: Visual Studio 2015
-          additional_flags: "/D_UNICODE /DUNICODE"
-
         # Exclude unwanted coverage configurations
         - coverage: 1
           platform: Win32
 
-        - coverage: 1
-          os: Visual Studio 2015
-
         - coverage: 1
           configuration: Release
 
@@ -54,9 +44,6 @@ matrix:
         - examples: 1
           platform: Win32
 
-        - examples: 1
-          os: Visual Studio 2015
-
         - examples: 1
           configuration: Release