Update django-environ to 0.5.0

[pyup-bot]

This PR updates django-environ from 0.4.5 to 0.5.0.

Changelog

0.5.0

--------------------------
Added
+++++
- Support for Django 2.1 & 2.2
- Added tox.ini targets
- Added secure redis backend URLs via ``rediss://``
- Add ``cast=str`` to ``str()`` method

Fixed
+++++
- Fixed misspelling in the documentation

Changed
+++++++
- Validate empty cache url and invalid cache schema
- Set ``long_description_content_type`` in setup
- Improved Django 1.11 database configuration support

Links

• PyPI: https://pypi.org/project/django-environ
• Changelog: https://pyup.io/changelogs/django-environ/
• Repo: https://github.com/joke2k/django-environ

[pyup-bot]

Closing this in favor of #418