Compiling mock-assembly in Visual Studio 2017 fails

[rprouse]

The solution builds fine in VS 2015, but fails in 2017 with the error,

Microsoft.NuGet.targets(178,5): error : Your project is not referencing the ".NETFramework,Version=v2.0" framework. Add a reference to ".NETFramework,Version=v2.0" in the "frameworks" section of your project.json, and then re-run NuGet restore.

I am pretty sure this is because of the .NET Standard project in the same directory. I believe the fix is to add a project.json file like we did in the NUnit Framework solution.