Bump django from 2.1.10 to 2.1.11

Bumps [django](https://github.com/django/django) from 2.1.10 to 2.1.11.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.1.10...2.1.11)

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

requirements.txt

@@ -4,7 +4,7 @@ celery==4.2.1
 # click==7.0
 cryptography==2.5
 dj-database-url==0.5.0
-django==2.1.10
+django==2.1.11
 django-celery-beat==1.4.0
 # django-celery-monitor==1.1.  # => https://pypi.org/project/django-celery-monitor/#history
 django-choices==1.6.2