version 1.1.01 you can use font awesome icons to replace the calendar icon in the header. Simply make sure you check the "use font awesome icon" option.
If your theme does not include the font awesome css file, you can select "include font awesome css file". This option will load the font awesome css file in your theme. If your theme already includes this file, you should not load it again.
A screenshot of the widget which uses font awesome icon in the header: