Bump django-debug-toolbar from 1.8 to 1.11.1

Bumps [django-debug-toolbar](https://github.com/jazzband/django-debug-toolbar) from 1.8 to 1.11.1.
- [Release notes](https://github.com/jazzband/django-debug-toolbar/releases)
- [Changelog](https://github.com/jazzband/django-debug-toolbar/blob/1.11.1/docs/changes.rst)
- [Commits](jazzband/django-debug-toolbar@1.8...1.11.1)

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

requirements-dev.txt

@@ -1,5 +1,5 @@
 -r requirements.txt
 factory-boy==2.11.1
 coverage==4.4.1
-django-debug-toolbar==1.8
+django-debug-toolbar==1.11.1
 coveralls==1.2.0