Bump certifi from 2020.4.5.1 to 2020.6.20

Bumps [certifi](https://github.com/certifi/python-certifi) from 2020.4.5.1 to 2020.6.20.
- [Release notes](https://github.com/certifi/python-certifi/releases)
- [Commits](certifi/python-certifi@2020.04.05.1...2020.06.20)

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

requirements.txt

@@ -1,4 +1,4 @@
-certifi==2020.4.5.1
+certifi==2020.6.20
 chardet==3.0.4
 idna==2.10
 requests==2.24.0