Change 'Update'-button visibility on change qty event.

Author: likemusic

app/code/Magento/Checkout/view/frontend/web/js/sidebar.js

@@ -105,6 +105,13 @@ define([
                 self._showItemButton($(event.target));
             };
 
+            /**
+             * @param {jQuery.Event} event
+             */
+            events['change ' + this.options.item.qty] = function (event) {
+                self._showItemButton($(event.target));
+            };
+
             /**
              * @param {jQuery.Event} event
              */