Drop .NET Core 2.1 SDK - Githubissues

This pull-request removes netcoreapp2.1 from the list of target frameworks (see https://github.com/bjorkstromm/depends/pull/23#issuecomment-950395889).

Two small additions I also added:

Set the default verbosity level to Information (instead of Trace)
Ignore a warning about MSBuild not supporting the target framework (in the same way as Buildalyzer, see comment in code)

If you feel any of these extra changes are unnecessary, I could of course revert them as well.

bjorkstromm / depends