Update django to 3.0.3

[pyup-bot]

This PR updates Django from 3.0.2 to 3.0.3.

Changelog

3.0.3

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

*February 3, 2020*

Django 3.0.3 fixes a security issue and several bugs in 3.0.2.

CVE-2020-7471: Potential SQL injection via ``StringAgg(delimiter)``
===================================================================

:class:`~django.contrib.postgres.aggregates.StringAgg` aggregation function was
subject to SQL injection, using a suitably crafted ``delimiter``.

Bugfixes
========

* Fixed a regression in Django 3.0 that caused a crash when subtracting
``DateField``, ``DateTimeField``, or ``TimeField`` from a ``Subquery()``
annotation (:ticket:`31133`).

* Fixed a regression in Django 3.0 where ``QuerySet.values()`` and
``values_list()`` crashed if a queryset contained an aggregation and
``Exists()`` annotation (:ticket:`31136`).

* Relaxed the system check added in Django 3.0 to reallow use of a sublanguage
in the :setting:`LANGUAGE_CODE` setting, when a base language is available in
Django but the sublanguage is not (:ticket:`31141`).

* Added support for using enumeration types ``TextChoices``,
``IntegerChoices``, and ``Choices`` in templates (:ticket:`31154`).

* Fixed a system check to ensure the ``max_length`` attribute fits the longest
choice, when a named group contains only non-string values (:ticket:`31155`).

* Fixed a regression in Django 2.2 that caused a crash of
:class:`~django.contrib.postgres.aggregates.ArrayAgg` and
:class:`~django.contrib.postgres.aggregates.StringAgg` with ``filter``
argument when used in a ``Subquery`` (:ticket:`31097`).

* Fixed a regression in Django 2.2.7 that caused
:meth:`~django.db.models.Model.get_FOO_display` to work incorrectly when
overriding inherited choices (:ticket:`31124`).

* Fixed a regression in Django 3.0 that caused a crash of
``QuerySet.prefetch_related()`` for ``GenericForeignKey`` with a custom
``ContentType`` foreign key (:ticket:`31190`).


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

Links

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

[coveralls]

Coverage remained the same at 100.0% when pulling ea8b92b on pyup-update-django-3.0.2-to-3.0.3 into 3cd1144 on master.