Incorrect - Content-Length

`headers['Content-Length']` is incorrect for some characters.
You can try this with a little experiment.

```javascript
> new Buffer('English', 'utf8').length
7
> 'English'.length
7
> new Buffer('ひらかな', 'utf8').length
12
> 'ひらかな'.length
4
```

I recommend you fix this by encoding the content into node.js Buffer before measure its length.