Bump certifi from 2017.7.27.1 to 2019.6.16

Bumps [certifi](https://github.com/certifi/python-certifi) from 2017.7.27.1 to 2019.6.16.
- [Release notes](https://github.com/certifi/python-certifi/releases)
- [Commits](certifi/python-certifi@2017.07.27.1...2019.06.16)

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

Author: dependabot-preview[bot]

requirements.txt

@@ -1,7 +1,7 @@
 alembic==1.1.0
 Babel==2.7.0
 blinker==1.4
-certifi==2017.7.27.1
+certifi==2019.6.16
 chardet==3.0.4
 click==7.0
 dominate==2.4.0