Upgrade node to 18

[Thovi98]

Problem

• Description of why you made this PR

Closes https://github.com/YunoHost-Apps/audiobookshelf_ynh/issues/118

Solution

• And how do you fix that problem

PR Status

• [ ] Code finished and ready to be reviewed/tested
• [ ] The fix/enhancement were manually tested (if applicable)

Automatic tests

Automatic tests can be triggered on https://ci-apps-dev.yunohost.org/ after creating the PR, by commenting "!testme", "!gogogadgetoci" or "By the power of systemd, I invoke The Great App CI to test this Pull Request!". (N.B. : for this to work you need to be a member of the Yunohost-Apps organization)

[Thovi98]

!testme

[yunohost-bot]

:carousel_horse:

[yunohost-bot]

Living in the future, are we?