Added Clang 4.0 and VC 2015 and 2017 tests

.appveyor.yml

@@ -2,6 +2,8 @@ clone_folder: c:\dev\glm-cmake
 
 os:
   - Visual Studio 2013
+  - Visual Studio 2015
+  - Visual Studio 2017
 
 platform:
   - x86

.travis.yml

@@ -36,10 +36,10 @@ matrix:
         apt:
           sources:
             - ubuntu-toolchain-r-test
-            - llvm-toolchain-precise-5.0
+            - llvm-toolchain-precise-4.0
           packages:
-            - clang-5.0
-      env: COMPILER=clang++-5.0
+            - clang-4.0
+      env: COMPILER=clang++-4.0
 compiler:
   - clang