Bump django from 2.1 to 2.1.11

Bumps [django](https://github.com/django/django) from 2.1 to 2.1.11.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/2.1...2.1.11)

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

requirements.txt

@@ -1,4 +1,4 @@
-Django==2.1
+Django==2.1.11
 django-autocomplete-light==3.3.2
 pytz==2018.5
 simplejson==3.16.0