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] <support@dependabot.com>

requirements.txt

@@ -1,5 +1,5 @@
 bcrypt==3.1.7
-certifi==2019.11.28
+certifi==2020.4.5.1
 cffi==1.14.0
 chardet==3.0.4
 colander==1.7.0