Doesn't work with "git worktree" creating working trees

[tpunder]

I noticed that gr doesn't work with a git worktree created working tree. I get an error saying Missing .git directory. The error is accurate since there is no .git directory. Instead git worktree creates a .git file with contents that looks like

gitdir: /path/to/myproject/.git/worktrees/myproject-somebranch

It would be cool if gr played nicely with git worktree!

Information about git worktree here: https://git-scm.com/docs/git-worktree

[tpunder]

The error I'm seeing comes from here:

gr/plugins/status.js

Line 33 in 51b00b0

style('Missing .git directory', 'red')

Looks like the logic of this function needs to be changed:

gr/lib/command-requirements.js

Line 5 in 51b00b0

git: function(req) {