Add customer email to Cancelled Order recipient list

wc_cancelled_order_add_customer_email.php

<?php

/* 
 * Add customer email to Cancelled Order recipient list
 */
 function wc_cancelled_order_add_customer_email( $recipient, $order ){
     return $recipient . ',' . $order->billing_email;
 }
 add_filter( 'woocommerce_email_recipient_cancelled_order', 'wc_cancelled_order_add_customer_email', 10, 2 );