docs(async): edit async

docs/object.md

@@ -874,7 +874,7 @@ function* entries(obj) {
 // 非Generator函数的版本
 function entries(obj) {
   let arr = [];
-  for (key of Object.keys(obj)) {
+  for (let key of Object.keys(obj)) {
     arr.push([key, obj[key]]);
   }
   return arr;