Bump requests from 2.19.1 to 2.20.0

Bumps [requests](https://github.com/psf/requests) from 2.19.1 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@v2.19.1...v2.20.0)

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

requirements.txt

@@ -12,7 +12,7 @@ MarkupSafe==1.0
 pyasn1==0.4.3
 pyasn1-modules==0.2.2
 pytz==2018.4
-requests==2.19.1
+requests==2.20.0
 rsa==3.4.2
 six==1.11.0
 urllib3==1.23