Bump sphinx from 3.5.4 to 4.1.0

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.5.4 to 4.1.0.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/4.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.5.4...v4.1.0)

---
updated-dependencies:
- dependency-name: sphinx
  dependency-type: direct:development
  update-type: version-update:semver-major
...

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

pyproject.toml

@@ -28,7 +28,7 @@ black = {version = "^20.8b1",allow-prereleases = true}
 pytest-cov = "^2.11.1"
 jsonschema = "^3.2.0"
 pylint = "^2.9.3"
-sphinx = "^3.5.3"
+sphinx = "^4.1.0"
 sphinx-autoapi = "^1.8.1"
 sphinx-rtd-theme = "^0.5.2"
 mypy = "^0.812"