Specify that MSBuild v14 use CoreClr RC1 for build

Former-commit-id: b6119e8ae168c0bd4d4041889da4a8dbdbbd6b39
Former-commit-id: 125af7e733ee6fbdf2cdffe2cc5c4e6f0031b8b0
Former-commit-id: 159e82547bfac124489b03606139a3277c9be09d

appveyor.yml

@@ -27,10 +27,9 @@ before_build:
 
     cd..
     
-build: 
+build_script:
-  project: ImageProcessor.sln
+- cmd: '"%programfiles(x86)%\MSBuild\14.0\Bin\amd64\MsBuild.exe" ImageProcessor.sln /verbosity:minimal /logger:"C:\Program Files\AppVeyor\BuildAgent\Appveyor.MSBuildLogger.dll" /p:RuntimeToolingDirectory="%USERPROFILE%\.dnx\runtimes\dnx-coreclr-win-x64.1.0.0-rc1-final"'
-  verbosity: minimal
+
-  
 test_script:
 - cmd: >-
     dnvm use 1.0.0-rc1-final -r coreclr -a x64