Bump django from 1.11.6 to 1.11.23

Bumps [django](https://github.com/django/django) from 1.11.6 to 1.11.23.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@1.11.6...1.11.23)

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

Author: dependabot[bot]

requirements.txt

@@ -1,6 +1,6 @@
 coverage==4.4.1
 dj-database-url==0.4.2
-Django==1.11.6
+Django==1.11.23
 gunicorn==19.7.1
 psycopg2==2.7.3.1
 pytz==2017.2