Fix DoesNotExistError in InvitePerson view

(cherry picked from commit 8513c8fd)

aleksis/core/tables.py

@@ -156,7 +156,7 @@ class PersonColumn(tables.Column):
     """Returns person object from given id."""
 
     def render(self, value):
-        return Person.objects.get(user__id=value)
+        return Person.objects.get(pk=value)
 
 
 class InvitationCodeColumn(tables.Column):