Change WooCommerce product tags to heirarchical

add_filter( 'woocommerce_taxonomy_args_product_tag', 'ljp_woocommerce_taxonomy_args_product_tag', 10, 1 );
 function ljp_woocommerce_taxonomy_args_product_tag( $array ) {
     $array['hierarchical'] = true;
     return $array;
 };