run docker pull once before CI tests

Merge pull request pure-fish#34 from mwilliammyers/master

Replace external commands with fish builtins where applicable

Merge pull request pure-fish#51 from pierrebeaucamp/master

Split fish_prompt into two seperate functions

Add support for python virtualenv

Add support for python virtualenv

Merge pull request pure-fish#48 from asymmetric/cmd-duration

Check for CMD_DURATION before calling __format_time

Add username and host to prompt in SSH sessions

Add support for custom process timeout threshold

Fix Git arrows and add support for failed process threshold

Fix test evaluation in Fish `2.5.0`

Merge pull request pure-fish#24 from bucaran/master

Remove useless fish shebang.