Bump django from 1.6 to 1.11.28

Bumps [django](https://github.com/django/django) from 1.6 to 1.11.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@1.6...1.11.28)

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

Author: dependabot[bot]

requirements.txt

@@ -1,4 +1,4 @@
-Django==1.6
+Django==1.11.28
 python-dateutil==2.1
 django-extensions
 MySQL-python==1.2.5