Update django-extra-views to 0.8.0

[pyup-bot]

There's a new version of django-extra-views available.
You are currently using 0.7.1. I have updated it to 0.8.0

Changelog

0.8

---

This version supports Django 1.6, 1.7, 1.8, 1.9 (latest minor versions), and Python 2.7, 3.4, 3.5 (latest minor versions).

• Added widgets attribute setting; allow to change form widgets in the ModelFormSetView.
• Added Django 1.9 support.
• Fixed get_context_data() usage of *args, **kwargs.
• Fixed silent overwriting of ModelForm fields to __all__.

Backwards-incompatible changes

- Dropped support for Django <= 1.5 and Python 3.3.
- Removed the ``extra_views.multi`` module as it had neither documentation nor
 test coverage and was broken for some of the supported Django/Python versions.
- This package no longer implicitly set ``fields = '__all__'``.
 If you face ``ImproperlyConfigured`` exceptions, you should have a look at the
 `Django 1.6 release notes`_ and set the ``fields`` or ``exclude`` attributes
 on your ``ModelForm`` or extra-views views.

.. _Django 1.6 release notes: https://docs.djangoproject.com/en/stable/releases/1.6/modelform-without-fields-or-exclude

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖