1.3.1

Enhancements
* Add some missing translations
* Add Serbian language

Fixes
* Fix broken redirect for empty `serverURL`
* Fix wrong variable type for HSTS maxAge
* Fix GitLab snippets showing up without being configured
* Fix Google's API after disabling Google+
* Fix broken PDF export

Contributors
* atachibana (translator)
* [Aurélien JANVIER](https://github.com/ajanvier) (translator)
* [Daan Sprenkels](https://github.com/dsprenkels) (translator)
* Farizrizaldy (translator)
* [Luclu7](https://github.com/Luclu7)
* Sylke Vicious (translator)
* [toshi0123](https://github.com/toshi0123) & okochi-toshiki
* [Turakar](https://github.com/Turakar)
* [Vladan](https://github.com/cvladan) (translator)
This tag has no release notes.