Allow live validation rules to be passed as array

This allows us to pass live validation rules as arrays, just like it's already possible in L4:

```php
Former::open('#')
      ->rules([
          'username' => ['required', 'alpha_num', 'between:3,64'],
          'password' => ['required', 'alpha_num', 'between:6,64'],
      ]);
```

Also made the already existing test now try with an array version.