Update appveyor.yml

Disable compilers to improve appveyor build performance

appveyor.yml

@@ -17,10 +17,10 @@ matrix:
     
 image:
   - Visual Studio 2013
-  - Visual Studio 2015
-  - Visual Studio 2017
+  #- Visual Studio 2015
+  #- Visual Studio 2017
   - Visual Studio 2019
-  - MinGW  
+  #- MinGW  
     
 platform:
   - Win32