Bump requests from 2.11.1 to 2.20.0

Bumps [requests](https://github.com/requests/requests) from 2.11.1 to 2.20.0.
- [Release notes](https://github.com/requests/requests/releases)
- [Changelog](https://github.com/psf/requests/blob/master/HISTORY.md)
- [Commits](psf/requests@v2.11.1...v2.20.0)

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

Author: dependabot[bot]

requirements.txt

@@ -2,7 +2,7 @@
 Django==2.0.7
 psycopg2==2.8.6
 oauthlib==2.0.0
-requests==2.11.1
+requests==2.20.0
 requests-oauthlib==0.6.2
 PyJWT==1.5.3
 gunicorn==19.6.0