Arr::path() does not work for numerical string indexes with leading 0's

## Arr::path() does not work for numerical string indexes with leading 0's

The following doesn't work.

```
$array = [
  'foo' => [
    '123' => 'bar'
  ]
];

$this->assertEquals('bar', Arr::path($array, 'foo.123'));
```

Write a test! Just copy and paste :point_up: