code: func (menu *Menu) SetMenu(buttons []*Button) error {
  	accessToken, err := menu.GetAccessToken()
  	if err != nil {
  		return err
  	}
  
  	uri := fmt.Sprintf("%s?access_token=%s", menuCreateURL, accessToken)
  	reqMenu := &reqMenu{
  		Button: buttons,
  	}
  
  	response, err := util.PostJSON(uri, reqMenu)
  	if err != nil {
  		return err
  	}
  
  	return util.DecodeWithCommonError(response, "SetMenu")
  }
docs: //SetMenu 设置按钮