www/py-dj21-django-filter: Update to 2.1.0

Changelog:

• Fixed a regression in FilterView introduced in 2.0. An empty QuerySet was incorrectly used whenever the FilterSet was unbound (i.e. when there were no GET parameters). The correct, pre-2.0 behaviour is now restored.

• A workaround was to set strict=False on the FilterSet. This is no longer necessary, so one may restore strict behaviour as desired.

• Added IsoDateTimeFromToRangeFilter. Allows From-To filtering using ISO-8601 formatted dates.

https://github.com/carltongibson/django-filter/releases/tag/2.1.0

Approved by: mentors (implicit)