Bump sphinx from 3.4.3 to 3.5.3

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.4.3 to 3.5.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](https://github.com/sphinx-doc/sphinx/commits)

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

Author: dependabot-preview[bot]

poetry.lock

@@ -28,7 +28,7 @@ black = {version = "^20.8b1",allow-prereleases = true}
 pytest-cov = "^2.11.1"
 jsonschema = "^3.2.0"
 pylint = "^2.6.0"
-sphinx = "^3.4.3"
+sphinx = "^3.5.3"
 sphinx-autoapi = "^1.7.0"
 sphinx-rtd-theme = "^0.5.1"
 mypy = "^0.800"