can we give up getter and setter syntax?
![image](https://user-images.githubusercontent.com/8686739/91534040-7730f800-e943-11ea-8cd5-1c4b7de8aab4.png)
we can do it the same, and koa code size is decreased, for example；
```js
module.exports = {
... some code ...

  get message() {
  },
  set message(msg = null) {
    if (msg) {
      this.res.statusMessage = msg;
    } else {
      return this.res.statusMessage || statuses[this.status];
    }
  },

... some code ...
}
```