On response header, Transfer-Encoding is always chunked

It's seems that if i use this package, `Content-Length` is never set and `Transfer-Encoding` is equal to `chunked`. 
Is it normal ?

My fix : setting the **Content-Length** juste before calling **send**
```
const data = JSON.parse(body);

data.moreInfo = 'tada!';

....

res.set('Content-Length', Buffer.byteLength(JSON.stringify(data), 'utf-8'));

send(JSON.stringify(data));
```