docs: fix async

docs/source/en/core/error-handling.md

@@ -148,7 +148,7 @@ If you want a customized 404 response, you only need to create a middleware to h
 ```js
 // app/middleware/notfound_handler.js
 module.exports = () => {
-  return async notFoundHandler(ctx, next) {
+  return async function notFoundHandler(ctx, next) {
     await next();
     if (ctx.status === 404 && !ctx.body) {
       if (ctx.acceptJSON) {

docs/source/en/tutorials/restful.md

@@ -157,7 +157,7 @@ class TopicController extends Controller {
     // status = 422 exception will be thrown if not passing the parameter validation
     ctx.validate(createRule);
     // call service to create a topic
-    const id = yield ctx.service.topics.create(ctx.request.body);
+    const id = await ctx.service.topics.create(ctx.request.body);
     // configure the response body and status code
     ctx.body = {
       topic_id: id,

docs/source/zh-cn/core/error-handling.md

@@ -146,7 +146,7 @@ module.exports = {
 ```js
 // app/middleware/notfound_handler.js
 module.exports = () => {
-  return async notFoundHandler(ctx, next) {
+  return async function notFoundHandler(ctx, next) {
     await next();
     if (ctx.status === 404 && !ctx.body) {
       if (ctx.acceptJSON) {

docs/source/zh-cn/tutorials/restful.md

@@ -158,7 +158,7 @@ class TopicController extends Controller {
     // 如果参数校验未通过，将会抛出一个 status = 422 的异常
     ctx.validate(createRule);
     // 调用 service 创建一个 topic
-    const id = yield ctx.service.topics.create(ctx.request.body);
+    const id = await ctx.service.topics.create(ctx.request.body);
     // 设置响应体和状态码
     ctx.body = {
       topic_id: id,