Bump django from 2.1.7 to 2.1.9

Bumps [django](https://github.com/django/django) from 2.1.7 to 2.1.9.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.1.7...2.1.9)

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

requirements.txt

@@ -1,6 +1,6 @@
 boto3==1.4.8
 dj-database-url==0.4.2
-django==2.1.7
+django==2.1.9
 django-debug-toolbar==1.10.1
 django-rest-framework==0.1.0
 django_storages==1.6.5