Update django to 3.0.2

[pyup-bot]

This PR updates Django from 3.0.1 to 3.0.2.

Changelog

3.0.2

==========================

*January 2, 2020*

Django 3.0.2 fixes several bugs in 3.0.1.

Bugfixes
========

* Fixed a regression in Django 3.0 that didn't include columns referenced by a
``Subquery()`` in the ``GROUP BY`` clause (:ticket:`31094`).

* Fixed a regression in Django 3.0 where ``QuerySet.exists()`` crashed if a
queryset contained an aggregation over a ``Subquery()`` (:ticket:`31109`).

* Fixed a regression in Django 3.0 that caused a migration crash on PostgreSQL
10+ when adding a foreign key and changing data in the same migration
(:ticket:`31106`).

* Fixed a regression in Django 3.0 where loading fixtures crashed for models
defining a :attr:`~django.db.models.Field.default` for the primary key
(:ticket:`31071`).


==========================

Links

• PyPI: https://pypi.org/project/django
• Changelog: https://pyup.io/changelogs/django/
• Homepage: https://www.djangoproject.com/

[coveralls]

Coverage remained the same at 87.803% when pulling c0d9db4 on pyup-update-django-3.0.1-to-3.0.2 into ee0bd80 on master.