Fatal error with PHP 7.4, using $this not in object context

Hi there,

I just updated PHP version to php 7.4 and I see your plugin gives fatal error:

Fatal error: Uncaught Error: Using $this when not in object context in /…/wp-content/plugins/taxonomy-terms-order/taxonomy-terms-order.php on line 123

Indeed, there is:

add_action( 'wp_ajax_update-custom-type-order-hierarchical', array(&$this, 'saveAjaxOrderHierarchical') );

but that is not inside any class. You should change this to

add_action( 'wp_ajax_update-custom-type-order-hierarchical', 'saveAjaxOrderHierarchical' );

and then it works