how to handle object keys beginning with a number

``` js
Qs.parse('a%5B12+v%5D=c&a%5Bfoo%5D=bar')
{a: {'12': 'c', foo: 'bar'}}
```

``` js
Qs.parse('a%5B12+v%5D=c');
{a: ['c']}
```

Is the above behavior expected? If yes, how to handle such keys?
