Update django to 2.0.7

[pyup-bot]

This PR updates Django from 2.0.6 to 2.0.7.

Changelog

2.0.7

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

*July 2, 2018*

Django 2.0.7 fixes several bugs in 2.0.6.

Bugfixes
========

* Fixed admin changelist crash when using a query expression without ``asc()``
or ``desc()`` in the page's ordering (:ticket:`29428`).

* Fixed admin check crash when using a query expression in
``ModelAdmin.ordering`` (:ticket:`29428`).

* Fixed ``__regex`` and ``__iregex`` lookups with MySQL 8 (:ticket:`29451`).

* Fixed migrations crash with namespace packages on Python 3.7
(:ticket:`28814`).


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

Links

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