Set PlatformToolset to VS2010 instead of Windows7.1SDK.

Author: end2endzone

ci/appveyor/emulate_appveyor.bat

@@ -6,9 +6,9 @@ set APPVEYOR=True
 set APPVEYOR_BUILD_FOLDER=%cd%
 set Configuration=Debug
 set Platform=x64
-REM set PlatformToolset=v100
+set PlatformToolset=v100
 REM set Platform=Win32
-set PlatformToolset=Windows7.1SDK
+REM set PlatformToolset=Windows7.1SDK
 
 echo Emulating appveyor's environment.
 echo APPVEYOR_BUILD_FOLDER set to '%APPVEYOR_BUILD_FOLDER%'