Bump requests from 2.3.0 to 2.20.0

Bumps [requests](https://github.com/psf/requests) from 2.3.0 to 2.20.0.
- [Release notes](https://github.com/psf/requests/releases)
- [Changelog](https://github.com/psf/requests/blob/master/HISTORY.md)
- [Commits](psf/requests@v2.3.0...v2.20.0)

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

requirements.txt

@@ -1,7 +1,7 @@
 Django==1.6.5
 django-storages==1.1.8
 boto==2.29.1
-requests==2.3.0
+requests==2.20.0
 gunicorn==19.5.0
 raven==5.0.0
 python-dateutil==1.5