Automatically add ASP.NET Core to the library path (#507)

Automatically add ASP.NET Core to the library path (#507)

Currently Impostor.Http is becoming an almost mandatory plugin. Because
it depends on ASP.Net, many people who fail to add the required path to
their config will run into an error. Help them by automatically adding
ASP.NET Core.

Also .NET updates every now and then and updating the version number in
the config.json is annoying me.

This commit uses the fact that ASP.NET Core DLL's are in a sibling folder
to the .NET runtime and should therefore work on most setups unless
they've installed ASP.NET Core in a very weird way.

* Fix casing

Co-authored-by: js6pak <kubastaron@hotmail.com>