MFH: r534393

www/py-bleach: Update to 3.1.5, Fix security issue

Changelog: https://github.com/mozilla/bleach/blob/v3.1.5/CHANGES

PR: 245943
Approved by: koobs (maintainer)
Security: 4c52ec3c-86f3-11ea-b5b4-641c67a117d8

Approved by: ports-secteam (joneum)