Update sphinx requirement from <3.4.0,>=3.0.3 to >=3.0.3,<3.5.0

Updates the requirements on [sphinx](https://github.com/sphinx-doc/sphinx) to permit the latest version.
- [Release notes](https://github.com/sphinx-doc/sphinx/releases)
- [Changelog](https://github.com/sphinx-doc/sphinx/blob/3.x/CHANGES)
- [Commits](sphinx-doc/sphinx@v3.0.3...v3.4.1)

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

doc-source/requirements.txt

@@ -3,7 +3,7 @@ default-values>=0.2.0
 domdf-sphinx-theme>=0.3.0
 extras-require>=0.2.0
 seed-intersphinx-mapping>=0.1.1
-sphinx<3.4.0,>=3.0.3
+sphinx>=3.0.3,<3.5.0
 sphinx-autofixture>=0.1.0
 sphinx-click>=2.5.0
 sphinx-copybutton>=0.2.12