install snappdf, since its not included by default anymore

[rndmh3ro]

Problem

install snappdf, since it isn't included by default anymore since 5.5.12: https://invoiceninja.github.io/docs/self-host-troubleshooting/#pdf-conversion-issues

Solution

• install it

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)

[rndmh3ro]

!testme

[yunohost-bot]

Fingers crossed!