Force Line Break

This does not depend on our plugin. WordPress prevents the use of HTML code in widget titles. You may notice the same thing happens with WP native text widgets.
A workaround may be to perform a text replacement on the title. In example, put [br] in your widget title, and add the following code snippet (not tested) in your theme’s functions.php or in a custom plugin:

add_filter( 'widget_title', 'my_widget_title', 10, 3 );
function my_widget_title( $title ) {
  $title = str_replace( "[br]", "<br/>", $title );
  return $title;
}