Update ServiceStack.Mvc.Tests.csproj

change nuget.targets to NuGet.targets
Update ServiceStack.Razor.Tests.csproj

change nuget.targets to NuGet.targets
Update ServiceStack.Server.Tests.csproj

change nuget.targets to NuGet.targets for linux
Update ServiceStack.RazorHostTests.csproj

change nuget.targets to NuGet.targets for linux
Merge pull request #910 from angelcolmenares/master

change nuget.targets to NuGet.targets for linux