[Fix Bug] Error when trying validate (getSize) a value of specific array...

```php
// rules
$rules = array(
 'child.name'   => 'required',
 'child.age'    => 'required|numeric|between:1,11',
 'child.gender' => 'required',
);

// dump Input::all()
array(1) {
  ["child"]=>
  array(3) {
    ["name"]=>
    string(4) "test"
    ["age"]=>
    string(2) "10"
    ["gender"]=>
    string(4) "male"
  }
}
```

```
// it will return an error :
ErrorException
Undefined index: child.age
```