Fix typo in vendor/django-debug-toolbar

Typo was introduced in
https://github.com/openhatch/oh-mainline/commit/e641408564fb9dde26083d510fb0a9ac591a1251
by Asheesh L.
Merge pull request #1484 from onceuponatimeforever/typo_in_django_debug_toolbar

Fix typo in vendor/django-debug-toolbar