Add images to assets manifest

assets/build/util/promisify.js

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+/**
+ * Node-style asynchronous function.
+ *
+ * @callback nodeAsyncCallback
+ * @param {string|null} err
+ * @param {*} data
+ */
+/**
+ * Promisify node-style asynchronous functions
+ *
+ * @param  {nodeAsyncCallback} fn - Function with node-style callback
+ * @param  {this} [scope] - Scope to which the function should be bound. Default: fn
+ * @returns {Promise} - An instance of Promise
+ */
+module.exports = (fn, scope) => function callback() {
+  const args = [].slice.call(arguments);
+  return new Promise((resolve, reject) => {
+    args.push((err, data) => (err === null ? resolve(data) : reject(err)));
+    return fn.apply(scope || fn, args);
+  });
+};