Bump django from 1.7.10 to 1.11.28 in /requirements

Bumps [django](https://github.com/django/django) from 1.7.10 to 1.11.28.
- [Release notes](https://github.com/django/django/releases)
- [Commits](https://github.com/django/django/compare/1.7.10...1.11.28)

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

requirements/requirements.txt

@@ -6,7 +6,7 @@ django-autoslug==1.9.3
 django-extensions==1.5.7
 django-image-cropping==1.0.2
 django-localflavor==1.1
-Django==1.7.10
+Django==1.11.28
 easy-thumbnails==2.2
 eav-django==1.4.7
 gunicorn==19.3.0