Bump six from 1.12.0 to 1.13.0

Bumps [six](https://github.com/benjaminp/six) from 1.12.0 to 1.13.0.
- [Release notes](https://github.com/benjaminp/six/releases)
- [Changelog](https://github.com/benjaminp/six/blob/master/CHANGES)
- [Commits](benjaminp/six@1.12.0...1.13.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

requirements.txt

@@ -26,7 +26,7 @@ python-dateutil==2.8.1
 redis==3.3.11
 requests==2.22.0
 simplejson==3.16.0
-six==1.12.0
+six==1.13.0
 transaction==2.4.0
 translationstring==1.3
 ujson==1.35