Swiss French QWERTZ keyboard: alt-G conflict?

### Is this a hackmd.io issue?

- [x] Yes, the bug happens on https://hackmd.io
- [ ] No. If it's a self-hosted CodiMD instance, please fire up the issue in the repo of CodiMD: https://github.com/hackmdio/codimd

### Read our Official tutorial

It's on https://hackmd.io/c/tutorials/

或是中文版 https://hackmd.io/c/tutorials-tw/

### What's the problem
On osx 10.13.6, with a Swiss French QWERTZ keyboard, In the editor on the left side, when I'm hitting alt-G in order to call the "@", HackMD shows me Jump to line instead. I'm relating a lot with "@" and it's really slow me down in my current workflow, especially now with the new @mention feature.
I've checked the prefs but I couldn't find any option to tweak this behaviour

#### Current behaviour

> Screenshot (optional)

Provide steps to reproduce:

1. Go to 'Edit window'
2. Click on '.alt-G' in order to get the "@" character
3. you get the "Jump to line" function instead with a Swiss French QWERTZ keyboard setup
If possible, create a note with reproducible content and share the link with us.

e.g. note link: https://hackmd.io/features

#### Expected behaviour
alt-G should behave as expected and delivers the "@" character instead of the "Jump to line" function

#### Environment

I use HackMD on:

**Desktop**
- OS: macOS 10.13.6
- Browser: firefox
- Browser Version: [74.0]