Remove custom colours from gitconfig

* They don't play nice with the Solarized colour scheme
Use PATH in fish config instead of fish_user_paths

* fish_user_paths seems to be causing fidhd to crap out and eventually
  end up making fish stop working until the fishd.whatever file is
  deleted
Use colors in grep (dunno how it was working previously)
Use rbenv's new fish support

* Might need to be changed now since 0.4.0 is up on homebrew