theme: vi-git-untracked: use 'sed q1' and `git status --porcelain`
theme: vi-git-untracked: use 'sed q1' and `git status --porcelain`

This speeds up detecting of untracked files.

btw: `git status --porcelain` is as fast as `ls-files` with `--directory`.

blueyed/oh-my-zsh,blueyed/oh-my-zsh,blueyed/oh-my-zsh