fix: you_are_in_preview_mode wrong german translation

[OtavioStasiak]

Proposed changes

we have a wrong German translation and to correct it we need to change the sentence "Sie befinden dich im Vorschaumodus" to "Sie befinden sich im Vorschaumodus".

Issue(s)

https://rocketchat.atlassian.net/browse/SUP-681

How to test or reproduce

Screenshots

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves a current function)
• New feature (non-breaking change which adds functionality)
• Documentation update (if none of the other choices apply)

Checklist

• I have read the CONTRIBUTING doc
• I have signed the CLA
• Lint and unit tests pass locally with my changes
• I have added tests that prove my fix is effective or that my feature works (if applicable)
• I have added necessary documentation (if applicable)
• Any dependent changes have been merged and published in downstream modules

Further comments

[CLAassistant]

All committers have signed the CLA.