Scaling does not take height into consideration.

I'm trying to scale an image without keeping the original ratio.

``` javascript
image.scale({
    width: 1000,
    height: 500
});
```

So, for instance, if an image has the dimensions `2000 x 800` before scaling, after calling the scale function as indicated above, the resulted image has the dimensions `1000 x 400` instead of `1000 x 500`.
