Update django to 1.11.17

[pyup-bot]

This PR updates Django from 1.11.16 to 1.11.17.

Changelog

1.11.17

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

*December 3, 2018*

Django 1.11.17 fixes several bugs in 1.11.16 and adds compatibility with
Python 3.7.

Bugfixes
========

* Prevented repetitive calls to ``geos_version_tuple()`` in the ``WKBWriter``
class in an attempt to fix a random crash involving ``LooseVersion`` since
Django 1.11.14 (:ticket:`29959`).


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

Links

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