Bump certifi from 2019.11.28 to 2020.4.5.1

Bumps [certifi](https://github.com/certifi/python-certifi) from 2019.11.28 to 2020.4.5.1.
- [Release notes](https://github.com/certifi/python-certifi/releases)
- [Commits](https://github.com/certifi/python-certifi/commits)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -3,7 +3,7 @@ argh==0.26.2
 Babel==2.8.0
 backports-abc==0.5
 backports.ssl-match-hostname==3.7.0.1
-certifi==2019.11.28
+certifi==2020.4.5.1
 chardet==3.0.4
 docutils==0.16
 futures==3.1.1