Prevent install script from exploding when password contains a special chars

[alexAubin]

Problem

cf https://forum.yunohost.org/t/invoiceninja-5-failing-install-on-web-admin/20612

Solution

Wrap var in quotes

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]

Thanks!