How to auto update woocommerce cart when quantity is changed?

Solution: 

It is very easy to update your woocommerce cart page automatically when quantity is changed.
To do this open your functions.php file and write down the following code.

add_action( 'woocommerce_after_cart', 'mycart_auto_update' );

function mycart_auto_update() {
    echo '<script>
    jQuery(document).ready(function($) 

   {
         $(".woocommerce-cart-form").find(".qty").on("change", function()

              {
                    upd_cart_btn.trigger("click");
             });
    });
    </script>';
 }