Bump django-debug-toolbar from 2.1 to 2.2

Bumps [django-debug-toolbar](https://github.com/jazzband/django-debug-toolbar) from 2.1 to 2.2.
- [Release notes](https://github.com/jazzband/django-debug-toolbar/releases)
- [Changelog](https://github.com/jazzband/django-debug-toolbar/blob/master/docs/changes.rst)
- [Commits](jazzband/django-debug-toolbar@2.1...2.2)

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

requirements.txt

@@ -1,6 +1,6 @@
 coverage==5.0.3
 Django==1.11.27 # pyup: <2.0
-django-debug-toolbar==2.1
+django-debug-toolbar==2.2
 docutils==0.16
 freezegun==0.3.14
 django-formtools==2.2