add more rev types, don't panic when rev can't be found

[edude03]

Needed to upgrade vgo, excuse how bad the code is, this is my first type trying to write go, and to be honest, I only did enough to get it to work.

[edude03]

@adisbladis added the keep going flag. No idea if that's the right way to do it in go though.

[adisbladis]

Fixed some minor nits and squashed in: https://github.com/adisbladis/vgo2nix/commit/f1edebfb24e09c657efeb60cf50aeee835dda930

Thank you!