code: func (wxa *MiniProgram) fetchData(urlStr string, body interface{}) (response []byte, err error) {
  	var accessToken string
  	accessToken, err = wxa.GetAccessToken()
  	if err != nil {
  		return
  	}
  	urlStr = fmt.Sprintf(urlStr, accessToken)
  	response, err = util.PostJSON(urlStr, body)
  	return
  }
docs: // fetchData 拉取统计数据