Update github.com URL
Update github.com URL

The repo was moved from the 'microsoft' org to the 'dotnet' org.

rainersigwald/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,AndyGerlicher/msbuild,rainersigwald/msbuild,AndyGerlicher/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild,sean-gilliam/msbuild,rainersigwald/msbuild