Bump sphinx from 3.2.1 to 3.3.1

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.2.1 to 3.3.1.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.2.1...v3.3.1)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

requirements/dev.txt

@@ -39,7 +39,7 @@ requests==2.23.0          # via sphinx
 six==1.15.0               # via packaging, pip-tools, tox, virtualenv
 snowballstemmer==2.0.0    # via sphinx
 sphinx-issues==1.2.0      # via -r requirements/docs.in
-sphinx==3.2.1             # via -r requirements/docs.in, pallets-sphinx-themes, sphinx-issues, sphinxcontrib-log-cabinet
+sphinx==3.3.1             # via -r requirements/docs.in, pallets-sphinx-themes, sphinx-issues, sphinxcontrib-log-cabinet
 sphinxcontrib-applehelp==1.0.2  # via sphinx
 sphinxcontrib-devhelp==1.0.2  # via sphinx
 sphinxcontrib-htmlhelp==1.0.3  # via sphinx

requirements/docs.txt

@@ -22,7 +22,7 @@ requests==2.23.0          # via sphinx
 six==1.15.0               # via packaging
 snowballstemmer==2.0.0    # via sphinx
 sphinx-issues==1.2.0      # via -r requirements/docs.in
-sphinx==3.2.1             # via -r requirements/docs.in, pallets-sphinx-themes, sphinx-issues, sphinxcontrib-log-cabinet
+sphinx==3.3.1             # via -r requirements/docs.in, pallets-sphinx-themes, sphinx-issues, sphinxcontrib-log-cabinet
 sphinxcontrib-applehelp==1.0.2  # via sphinx
 sphinxcontrib-devhelp==1.0.2  # via sphinx
 sphinxcontrib-htmlhelp==1.0.3  # via sphinx