Update translation requests contact
# What does this PR do?
Updates the contact for translation requests to GuggerSylvain (@sgugger - if you're alright with that!)

## Before submitting
- [x] This PR fixes a typo or improves the docs (you can dismiss the other checks if that's the case).

## Who can review?
Documentation: @sgugger, @osanseviero 
_The documentation is not available anymore as the PR was closed or merged._<|||||>Doesn't look like I have merge privileges on this repo, could you merge it @sgugger?<|||||>Just waiting for the last green tick and will do so!