⬆️ Update dependencies and upgrade test projects to .NET 6

[roycornelissen]

I thought this project was due for some maintenance on its dependencies.

I also upgraded the test projects to net6.0. Even though aspnetcore3.1 is still officially supported until the end of 2022, I think many projects have already moved on to net5.0 or net6.0.

[nover]

Beautiful @roycornelissen - thanks for your continued work on this library :)

I see that appveyor is giving you a hard time. You have to apply a small fix to the appveyor CI file, you can see what I did over here to make it work:
skarpdev/dotnet-version-cli#93

[roycornelissen]

@nover Ah thanks for the heads up, I was already wondering if that would build without changes to the build scripts :)

Fixed!

[roycornelissen]

@nover I might add an extra target to the library for .NET6, because I think that will resolve #83

Update: well, almost, only System.Threading.ThreadPool still has an issue then. But I still added net5.0 and net6.0 as targets.

[nover]

@roycornelissen I believe that rapidcore has now been released as 0.27 - would you do the honors of upgrading the dependency in this PR - the w can kill the problem in #83 for good I believe.

[roycornelissen]

@nover Done, updated to latest Nuget dependencies, including RapidCore 0.27 :)

If you're OK, we can merge it

[nover]

💯