Bump sphinx from 3.0.3 to 3.0.4 in /requirements
Bump sphinx from 3.0.3 to 3.0.4 in /requirements

Bumps [sphinx](https://github.com/sphinx-doc/sphinx) from 3.0.3 to 3.0.4.
- [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/compare/v3.0.3...v3.0.4)

Signed-off-by: dependabot-preview[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@dependabot.com>
mozilla/addons-server,bqbn/addons-server,wagnerand/addons-server,diox/olympia,mozilla/addons-server,diox/olympia,wagnerand/addons-server,mozilla/olympia,bqbn/addons-server,bqbn/addons-server,diox/olympia,diox/olympia,eviljeff/olympia,mozilla/addons-server,wagnerand/addons-server,mozilla/addons-server,eviljeff/olympia,bqbn/addons-server,eviljeff/olympia,mozilla/olympia,wagnerand/addons-server,mozilla/olympia,eviljeff/olympia,mozilla/olympia