Update sphinx-autobuild to 2021.3.14

[pyup-bot]

This PR updates sphinx-autobuild from 0.7.1 to 2021.3.14.

Changelog

2020.09.01

-----------------------

* Adopt Calendar Versioning.
* Modernize codebase and require Python 3.6+.
* Directly depend on ``sphinx``.
* Rewritten documentation.
* Invoke sphinx via ``{sys.executable} -m sphinx`` instead of ``sphinx-build``.
* Trim dependencies down to only ``livereload`` and ``sphinx``.
* Drop custom adapter for ``watchdog``.
* Drop ``--poll`` flag.
* Drop single letter variants for flags that were specific to sphinx-autobuild.

Links

• PyPI: https://pypi.org/project/sphinx-autobuild
• Changelog: https://pyup.io/changelogs/sphinx-autobuild/
• Repo: https://github.com/executablebooks/sphinx-autobuild

[pyup-bot]

Closing this in favor of #462