Fix UMM versions and updates

[t0stiman]

The repository.json points to v5.0.0, while 6.3.1 is the newest version.
The info.json file in the newest UMM release has "Version": "0.0.0.0",.

Fixing these issues would make it possible to update RuntimeUnityEditor from the UMM GUI, which would be convenient

[ManlyMarco]

Can you open a PR with a fix?

[t0stiman]

done

[ManlyMarco]

This will need some sort of automation to keep being updated.