Appveyor: use correct names for project generators.

appveyor.yml

@@ -15,11 +15,11 @@ platform:
     - x64
 
 configuration:
-  - 2015
-  - 2013
-  - 2012
+  - 14 2015
+  - 12 2013
+  - 11 2012
   #- MinGW
-  - 2010 # only works for x86
+  - 10 2010 # only works for x86
 
 init:
 - if "%platform%" EQU "x64" ( for %%a in (2008 2010 MinGW) do ( if "%Configuration%"=="%%a" (echo "Skipping unsupported configuration" && exit /b 1 ) ) )