General maintenance release

- ⬆Update base image to 7.0.4
- ⬆Update php to 7.3.16-r0

Questions? Join our Discord server! https://discord.me/hassioaddons

[Full Changelog][changelog]

[changelog]: https://github.com/hassio-addons/addon-bookstack/compare/v0.2.1...v0.2.2