Assertion Error: Headers already sent
Code:
https://gist.github.com/haxxorsid/348169a3a6c93ee241dfdb8170709651
Run:
```
git clone https://gist.github.com/haxxorsid/348169a3a6c93ee241dfdb8170709651.git
cd 348169a3a6c93ee241dfdb8170709651
npm install
npm start
```
In browser: `http://localhost:3000/my-scale/resize/100/123?url=image.jpg`
It resizes image.jpg(without overwriting the file) to 100width & 123height and displays that in browser.

Error:
`AssertionError [ERR_ASSERTION]: headers have already been sent`

Can someone solve this issue for me. Maybe this issue is not at all related to koajs.