Update testtools to 2.4.0

[pyup-bot]

This PR updates testtools from 2.3.0 to 2.4.0.

Changelog

2.4.0

~~~~~

Improvements
------------

* Add support for Python 3.7, 3.8 and PyPy3.
(Hugo van Kemenade)

* Drop support for Python 3.4 (EOL).
(Jelmer Vernooij)

* Avoid using eval(). (Ross Burton)

* PyCharm IDE unittest detection compatibility fix.
(Adam Harwell)

* Drop support for Python 3.3 (EOL).
(Robert Collins)

* Spelling fixes. (Free Ekanayaka)

* Python 3.6 invalid escape sequence deprecation fixes. (Ville Skyttä)

Links

• PyPI: https://pypi.org/project/testtools
• Changelog: https://pyup.io/changelogs/testtools/
• Repo: https://github.com/testing-cabal/testtools

[coveralls]

Coverage remained the same at 90.385% when pulling b49a9e6 on pyup-update-testtools-2.3.0-to-2.4.0 into ea622e5 on master.

[pyup-bot]

Closing this in favor of #144