Description:
------------
I'm using the last version of the package: 2.0.10
The "collect" method returns elements in wrong order, always overwrites the first result with the last result.

Test script:
---------------
class job extends Collectable
{
	public $val;

	public function __construct($val){
    	    $this->val = $val;
	}
	public function run(){
	    'started ' .$this->val . PHP_EOL;    
	    sleep(1);
	    'finished ' .$this->val . PHP_EOL;		
	    $this->setGarbage();
	}
}

$p = new Pool(1);

$tasks = array(
    new job('job1'),
    new job('job2'),
    new job('job3'),
    new job('job4'),
    new job('job5')
);

foreach ($tasks as $task)
    $p->submit($task);

$p->shutdown();

$p->collect(function($checkingTask){
   $checkingTask->val;
});

Expected result:
----------------
job1
job2
job3
job4
job5

Actual result:
--------------
job5
job2
job3
job4
job5