Bump sphinx from 3.1.1 to 3.2.0

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.1.1 to 3.2.0.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.1.1...v3.2.0)

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

docs-requirements.txt

@@ -29,7 +29,7 @@ sniffio==1.1.0            # via -r docs-requirements.in
 snowballstemmer==2.0.0    # via sphinx
 sortedcontainers==2.2.2   # via -r docs-requirements.in
 sphinx-rtd-theme==0.5.0   # via -r docs-requirements.in
-sphinx==3.1.1             # via -r docs-requirements.in, sphinx-rtd-theme, sphinxcontrib-trio
+sphinx==3.2.0             # via -r docs-requirements.in, sphinx-rtd-theme, sphinxcontrib-trio
 sphinxcontrib-applehelp==1.0.2  # via sphinx
 sphinxcontrib-devhelp==1.0.2  # via sphinx
 sphinxcontrib-htmlhelp==1.0.3  # via sphinx