Remove bug in phpArray asserter.

Without this patch, it's not possible to write something like:
```php
$this->in(array(
         0 => array(
            0 => array(
	       1 => array('foo', 'bar')
	   ),
	   1 => array(1, new \mock\object())
         ),
         1 => 'foobar'
      )
   )
)
->then
   ->array[0][0][1]->isEqualTo(array('foo', 'bar'))
;
```