Bump requests from 2.12.5 to 2.20.0 in /requirements

Bumps [requests](https://github.com/requests/requests) from 2.12.5 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@v2.12.5...v2.20.0)

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

requirements/base.txt

@@ -39,7 +39,7 @@ pygal==2.3.0
 python-crontab==2.4.0
 Pygments==2.1.3
 reportlab==3.5.34
-requests==2.12.5
+requests==2.20.0
 simplegeneric==0.8.1
 six==1.10.0
 tinycss==0.4