Override route key name if $primaryKey is overridden

[Jared0430]

Currently, if you use a custom primary key on your model, you also have to override the getRouteKeyName() method, otherwise, the custom route key name doesn't get detected

This PR fixes this by also checking if the $primaryKey property has been set on your model

[bakerkretzmar]

Thanks, good catch 👍🏻 can you add a test for this, and also add getKeyName() since we should probably be checking that too? I can circle back and add a test here in the next week or two as well, no rush.

[Jared0430]

Added support for getKeyName() and some tests 👍

[bakerkretzmar]

Thanks a lot! I'll tag a release in the next day or two.