Bump requests from 2.18.4 to 2.20.0

Bumps [requests](https://github.com/requests/requests) from 2.18.4 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@v2.18.4...v2.20.0)

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

Author: dependabot[bot]

requirements.txt

@@ -17,7 +17,7 @@ pyasn1==0.3.2
 Pygments==2.2.0
 PyJWT==1.5.2
 pytz==2017.2
-requests==2.18.4
+requests==2.20.0
 six==1.10.0
 snowballstemmer==1.2.1
 Sphinx==1.6.3