Update sphinx to 1.7.9

[pyup-bot]

This PR updates Sphinx from 1.7.8 to 1.7.9.

Changelog

1.7.9

=====================================

Features added
--------------

* 5359: Make generated texinfo files reproducible by sorting the anchors

Bugs fixed
----------

* 5361: crashed on incremental build if document uses include directive

Links

• PyPI: https://pypi.org/project/sphinx
• Changelog: https://pyup.io/changelogs/sphinx/
• Homepage: http://sphinx-doc.org/

[coveralls]

Coverage remained the same at 100.0% when pulling f9e4405 on pyup-update-sphinx-1.7.8-to-1.7.9 into ddf8e45 on master.