WooCommerce Add Special Class to Free Products

gistfile1.txt

function itl_add_class_free_products( $price ) {
	$price = '<span class="amount free-product">' . __( 'Free!', 'woocommerce' ) . '</span>';
	return $price;
}
add_filter( 'woocommerce_variable_free_price_html',  'itl_add_class_free_products' );
add_filter( 'woocommerce_free_price_html',           'itl_add_class_free_products' );
add_filter( 'woocommerce_variation_free_price_html', 'itl_add_class_free_products' );