Just to make complete:
You dont have to change ibraries/gantry/features/font.php.
Now, we need to check and/or reedit this after every gantry upgrade.
Not true. You can easily override font.php.
All you need to do is to copy libraries/gantry/features/font.php into the features folder of your template.
That's the file you need to change now and it won't get overridden with every Gantry or template update.