Maintenance release:

- ⬆ Update Bookstack to v0.31.3
- ⬆ Update php to 7.3.26-r0

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

[Full Changelog][changelog]

[changelog]: https://github.com/hassio-addons/addon-bookstack/compare/v0.6.4...v0.7.0