Add a 'git fetch origin' alias -> 'gfeo'

[marcosdsanchez]

Add a 'git fetch origin' alias -> 'gfeo'

[mcornella]

git fetch by default already fetches only from the origin remote. I propose a gf alias because it's not used by any other plugin in the repo, so you can do gf upstream if you feel like it, while having the same behavior as your alias if you don't specify any remote.

This one is already included with PR #2790: https://github.com/robbyrussell/oh-my-zsh/pull/2790/files#diff-4ad2773a26526d0e361e66139c283099R255, so this PR can be closed. @ncanceill please add this PR to the list of closed/fixed.