Update appveyor.yml

Author: gabime

appveyor.yml

@@ -2,42 +2,6 @@ version: 1.0.{build}
 image: Visual Studio 2017
 environment:
   matrix:
-    - GENERATOR: '"Visual Studio 14 2015"'
-      BUILD_TYPE: Debug
-      BUILD_SHARED: 'OFF'
-      FATAL_ERRORS: 'ON'
-      WCHAR: 'OFF'
-      WCHAR_FILES: 'OFF'
-      BUILD_EXAMPLE: 'ON'
-      USE_STD_FORMAT: 'OFF'
-      CXX_STANDARD: 11
-    - GENERATOR: '"Visual Studio 14 2015"'
-      BUILD_TYPE: Release
-      BUILD_SHARED: 'OFF'
-      FATAL_ERRORS: 'ON'
-      WCHAR: 'ON'
-      WCHAR_FILES: 'OFF'
-      BUILD_EXAMPLE: 'ON'
-      USE_STD_FORMAT: 'OFF'
-      CXX_STANDARD: 11
-    - GENERATOR: '"Visual Studio 14 2015 Win64"'
-      BUILD_TYPE: Debug
-      BUILD_SHARED: 'OFF'
-      FATAL_ERRORS: 'ON'
-      WCHAR: 'ON'
-      WCHAR_FILES: 'OFF'
-      BUILD_EXAMPLE: 'ON'
-      USE_STD_FORMAT: 'OFF'
-      CXX_STANDARD: 11
-    - GENERATOR: '"Visual Studio 14 2015 Win64"'
-      BUILD_TYPE: Release
-      BUILD_SHARED: 'OFF'
-      FATAL_ERRORS: 'ON'
-      WCHAR: 'ON'
-      WCHAR_FILES: 'OFF'
-      BUILD_EXAMPLE: 'ON'
-      USE_STD_FORMAT: 'OFF'
-      CXX_STANDARD: 11
     - GENERATOR: '"Visual Studio 15 2017 Win64"'
       BUILD_TYPE: Debug
       BUILD_SHARED: 'OFF'