Bump django from 1.11 to 1.11.23 in /containers/backend (#458)

Bumps [django](https://github.com/django/django) from 1.11 to 1.11.23.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/1.11...1.11.23)

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

containers/backend/requirements.txt

@@ -1,4 +1,4 @@
-Django==1.11
+Django==1.11.23
 django-cors-middleware==1.3.1
 djangorestframework==3.6.2
 djangorestframework-jwt==1.10.0