Bump requests from 2.7.0 to 2.20.0

Bumps [requests](https://github.com/psf/requests) from 2.7.0 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@v2.7.0...v2.20.0)

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

Author: dependabot[bot]

requirements.txt

@@ -20,7 +20,7 @@ oauthlib==1.0.1
 Pillow==2.9.0
 psycopg2==2.6.1
 python-openid==2.2.5
-requests==2.7.0
+requests==2.20.0
 requests-oauthlib==0.5.0
 six==1.9.0
 sqlparse==0.1.16