Bump django from 2.2.9 to 2.2.18

Bumps [django](https://github.com/django/django) from 2.2.9 to 2.2.18.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.2.9...2.2.18)

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

Author: dependabot[bot]

requirements.txt

@@ -3,7 +3,7 @@ attrs==17.4.0
 client==0.0.1
 coverage==4.4.2
 dj-database-url==0.5.0
-Django==2.2.9
+Django==2.2.18
 django-widget-tweaks==1.4.1
 gunicorn==19.7.1
 mock==2.0.0