Bump django-debug-toolbar from 2.1 to 2.2 in /src/requirements

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](https://github.com/jazzband/django-debug-toolbar/compare/2.1...2.2)

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

src/requirements/dev.txt

@@ -1,6 +1,6 @@
 -r production.txt
 
-django-debug-toolbar==2.1
+django-debug-toolbar==2.2
 factory_boy==2.12.0
 coverage==4.5.4
 codecov==2.0.15