Fix "invalid escape sequence '\' (W605)"
Summary:
In python 3.6, using the \ char in a string that is not part of a
valid escape sequence will generate a Deprecation warning. For us it
means that flake8 is upset.
We use this in regex and in ascii art.
Reviewers: mmodell, Release-Engineering-Team
Reviewed By: mmodell, Release-Engineering-Team
Tags: Release-Engineering-Team
Differential Revision: https://phabricator.wikimedia.org/D1121