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] <support@github.com>

Author: dependabot[bot]

requirements-dev.txt

@@ -15,7 +15,7 @@ pyparsing==2.2.0
 pytest-cov==2.5.1
 pytest==3.2.3
 pytz==2017.3
-requests==2.18.4
+requests==2.20.0
 six==1.11.0
 stevedore==1.27.1
 urllib3==1.22

requirements.txt

@@ -11,7 +11,7 @@ pbr==3.1.1
 psutil==5.4.0
 pyparsing==2.2.0
 pytz==2017.3
-requests==2.18.4
+requests==2.20.0
 selenium==3.7.0
 six==1.11.0
 stevedore==1.27.1