Create a widget with Icons – fontawesome bug

Hello,

i want to create a new widget and this is one of my form options:

'icon' => array(
  'type' => 'icon',
  'label' => __('Select an icon', 'widget-form-fields-text-domain'),
),

In the wp backend I choise the facebook icon but I get a strange output:

fontawesome-facebook-square

But this should be right:

fa-facebook-square

I like your pagebuilder but that is a strange behavior.

How can I fix this?