Bump requests from 2.19.1 to 2.20.0

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

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

requirements.txt

@@ -30,7 +30,7 @@ pysam==0.14.1
 python-dateutil==2.7.3
 pytz==2018.4
 PyYAML==3.12
-requests==2.19.1
+requests==2.20.0
 scipy==1.0.1
 scrappie==1.3.3
 seaborn==0.8.1