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]>