Object turns into an array after unflattening

``` javascript
var flat = require("flat");

var data = {
"object": {"0": "a", "1": "b"}
};

console.log(flat.unflatten(flat.flatten(data)));
```

Outputs

``` javascript
{ object: [ 'a', 'b' ] }
```

Not sure how often people would use integers as object keys, but is a valid case nonetheless.

I realize that yes, you can pass `{object:true}` to unflatten, and it will not automatically assume it's an array, but then you get the opposite behavior. i.e. "Arrays turn into objects".

A more generic solution would be to use square brackets in the flattened format, where:

`object[0]`, and `object.0` imply different data structures.