test_translate_pattern fails on Python 3.7

Originally reported by michel on slack: https://the-asf.slack.com/archives/CBDNLQZM1/p1539697967000100

Cause:

https://docs.python.org/3/whatsnew/3.7.html:
Change re.escape() to only escape regex special characters instead of
escaping all characters other than ASCII letters, numbers, and '_'.
(Contributed by Serhiy Storchaka in bpo-29995.)