py-django: updated to 1.11.13

1.11.13:
Bugfixes
* Fixed a regression in Django 1.11.8 where altering a field with a unique constraint may drop and rebuild more foreign keys than necessary.
* Fixed crashes in django.contrib.admindocs when a view is a callable object, such as django.contrib.syndication.views.Feed.
* Fixed a regression in Django 1.11.12 where QuerySet.values() or values_list() after combining an annotated and unannotated queryset with union(), difference(), or intersection() crashed due to mismatching columns

(adam)