Bump sphinx-autobuild from 2020.9.1 to 2021.3.14

Bumps [sphinx-autobuild](https://github.com/executablebooks/sphinx-autobuild) from 2020.9.1 to 2021.3.14.
- [Release notes](https://github.com/executablebooks/sphinx-autobuild/releases)
- [Changelog](https://github.com/executablebooks/sphinx-autobuild/blob/main/NEWS.rst)
- [Commits](https://github.com/executablebooks/sphinx-autobuild/commits)

Signed-off-by: dependabot[bot] <support@github.com>

requirements-dev.txt

@@ -13,5 +13,5 @@ sphinx-issues==1.2.0
 sphinx-jinja==1.1.1
 sphinx-tabs==2.1.0
 sphinxcontrib-programoutput==0.17
-sphinx-autobuild==2020.9.1
+sphinx-autobuild==2021.3.14
 linuxdoc==20210324