Update django-braces to 1.15.0

[pyup-bot]

This PR updates django-braces from 1.12.0 to 1.15.0.

Changelog

1.15.0

* :support:`-` Formatted project with black
* :support:`-` Updated README
* :feature:`265` Drop old Python and Django versions, bring in newer ones

1.14.0

* :support:`260` Fixes the goshdang Travis tests.
* :support:`250` Include documentation Makefile and conf.py in source distribution.
* :support:`246` README more accurately explains the supported Django versions.

1.13.0

* :support:`243` Adds support for Python 3.7 and Django 2.1.
* :support:`244` Documentation link fix.
* :support:`236` Refines the Django and Python versions tested against.
* :support:`241` Fixes a documentation typo, "altenate" should be "alternate".

Links

• PyPI: https://pypi.org/project/django-braces
• Changelog: https://pyup.io/changelogs/django-braces/
• Repo: https://github.com/brack3t/django-braces/

[pyup-bot]

Closing this in favor of #1447