Updating a shared note result in an error

If we try to update a note that is not ours, but that we are allowed to edit, the note is edited but the API answers with a `403 Forbidden` answer:

```
$ hackmd-cli export --noteId jmYbFyeLQOyS2mwonYqCYw
aa
$ hackmd-cli notes update --noteId jmYbFyeLQOyS2mwonYqCYw --content="bb"
Update note content failed
Error: Received an error response (403 Forbidden) from HackMD
Code: 403
$ hackmd-cli export --noteId jmYbFyeLQOyS2mwonYqCYw
bb
```

This problem is on the hackmd API side, but I don't know on which repo to open the issue...

Reproduce the sequence with `hackmd-cli export` and `hackmd-cli notes update` for a shared note the user may edit. Then trace the notes update command and its HackMD API response handling; done means an allowed update no longer reports a 403, or the issue is confirmed to belong in the HackMD API repository.

Escrita pelo modelo de indexação a partir do texto da issue.