Fixed advice on invalid permissions on upload path

When running the checks, my upload path has wrong permissions, the advice could not fix it because it does not change the permission of this directory (only sub-directories).
```
Uploads directory setup correctly? ... no
  Try fixing it:
  sudo find /home/git/gitlab/public/uploads -type d -not -path /home/git/gitlab/public/uploads -exec chmod 0700 {} \;
  For more information see:
  doc/install/installation.md in section "GitLab"
  Please fix the error above and rerun the checks.
```

Executing this instead fixed the error :
```
sudo chmod 700 /home/git/gitlab/public/uploads
```

See merge request !2948