Fabian Homborg c242d923c9 sample_prompts/robbyrussell: Use fish_print_hg_root
This removes ~140ms from every single prompt.

When not in a git repo, this prompt now takes ~9ms, as opposed to
~150ms before.

Fixes #5266 harder.

[ci skip]
2018-11-30 20:59:53 +01:00
..