Build script no longer runs xUnit tests for .NET Core 2.0 target

[stakx]

From one recent build log - running dotnet xunit -nobuild -configuration Release -noshadow from inside the Moq.Tests project directory produces this message:

  Locating binaries for framework netcoreapp2.0...
  Running .NET Core 2.0 tests for framework netcoreapp2.0...
  The specified framework version '2.0' could not be parsed
  
  The specified framework 'Microsoft.NETCore.App', version '2.0' was not found.
  
    - Check application dependencies and target a framework version installed at:
  
        \
  
    - Alternatively, install the framework version '2.0'.

This seems to be the same issue as https://github.com/dotnet/cli/issues/7901. Not quite sure yet whether this will resolve itself, or what needs to be done.

In either case, it would be nice if Moq's build script at least emitted a warning.