Update 'build.cmd' to pull Sake from v2 NuGet feed.

Author: N. Taylor Mullen

build.cmd

@@ -17,7 +17,7 @@ copy %CACHED_NUGET% .nuget\nuget.exe > nul
 :restore
 IF EXIST packages\KoreBuild goto run
 .nuget\NuGet.exe install KoreBuild -ExcludeVersion -o packages -nocache -pre
-.nuget\NuGet.exe install Sake -version 0.2 -o packages -ExcludeVersion
+.nuget\NuGet.exe install Sake -ExcludeVersion -Source https://www.nuget.org/api/v2/ -Out packages
 
 IF "%SKIP_DNX_INSTALL%"=="1" goto run
 CALL packages\KoreBuild\build\dnvm upgrade -runtime CLR -arch x86