Update django to 2.0.8 (cookiecutter#1734)

This PR updates [django](https://pypi.org/project/django) from **2.0.7** to **2.0.8**.



<details>
  <summary>Changelog</summary>
  
  
   ### 2.0.8
   ```
   ==========================

*August 1, 2018*

Django 2.0.8 fixes a security issue and several bugs in 2.0.7.

CVE-2018-14574: Open redirect possibility in ``CommonMiddleware``
=================================================================

If the :class:`~django.middleware.common.CommonMiddleware` and the
:setting:`APPEND_SLASH` setting are both enabled, and if the project has a
URL pattern that accepts any path ending in a slash (many content management
systems have such a pattern), then a request to a maliciously crafted URL of
that site could lead to a redirect to another site, enabling phishing and other
attacks.

``CommonMiddleware`` now escapes leading slashes to prevent redirects to other
domains.

Bugfixes
========

* Fixed a regression in Django 2.0.7 that broke the ``regex`` lookup on MariaDB
  (even though MariaDB isn&#39;t officially supported) (:ticket:`29544`).

* Fixed a regression where ``django.template.Template`` crashed if the
  ``template_string`` argument is lazy (:ticket:`29617`).


==========================
   ```
   
  
</details>


 

<details>
  <summary>Links</summary>
  
  - PyPI: https://pypi.org/project/django
  - Changelog: https://pyup.io/changelogs/django/
  - Homepage: https://www.djangoproject.com/
</details>

{{cookiecutter.project_slug}}/requirements/base.txt

@@ -18,7 +18,7 @@ flower==0.9.2  # https://github.com/mher/flower
 
 # Django
 # ------------------------------------------------------------------------------
-django==2.0.7  # pyup: < 2.1  # https://www.djangoproject.com/
+django==2.0.8  # pyup: < 2.1  # https://www.djangoproject.com/
 django-environ==0.4.5  # https://github.com/joke2k/django-environ
 django-model-utils==3.1.2  # https://github.com/jazzband/django-model-utils
 django-allauth==0.36.0  # https://github.com/pennersr/django-allauth