Bump sphinx from 3.3.1 to 3.4.3 (#754)

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.3.1 to 3.4.3.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.3.1...v3.4.3)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: cjolowicz

{{cookiecutter.project_name}}/poetry.lock

@@ -34,7 +34,7 @@ safety = "^1.10.3"
 mypy = "^0.800"
 typeguard = "^2.9.1"
 xdoctest = {extras = ["colors"], version = "^0.15.2"}
-sphinx = "^3.3.1"
+sphinx = "^3.4.3"
 sphinx-autobuild = "^2020.9.1"
 pre-commit = "^2.10.0"
 flake8 = "^3.8.4"