Revert "Fix RemovedInDjango18Warning: `Manager.get_query_set` method should be renamed `get_queryset`"
Revert "Fix RemovedInDjango18Warning: `Manager.get_query_set` method should be renamed `get_queryset`"

This reverts commit 07a707566fe53c6caf4f50988d42546b8104a005.

merlin83/django-background-tasks