title: await promise return undefined?
body: <h3>Here is code :</h3>
  
  <pre><code>export const wxreq = (config) =&gt; {
  config.url = `${HTTP_HOST}${config.url}`;
  return new Promise((resolve, reject) =&gt; {
      return wepy.request(Object.assign(config, {
          async success (res) {
              // res is a promise, this promise is return  {data: 123}
              const responseFromMiddle = await res;
              return resolve(responseFromMiddle.data);
          },
          fail () {
              reject(new Error(`Request ${config.url} fail!`));
          },
          complete () {
              resolve();
          }
      }))
    })
  };
  </code></pre>
  
  <p>in vuejs life-cycle</p>
  
  <pre><code>async onReady () {
    cosnt res = wxreq(someCorrectConfig);
    console.log(res); // undefined; need to be 123 
  }
  </code></pre>
  
  <p>I'm very curious that why res is not defined？ please help~  so confused！ thx~</p>