Add class Phalcon\Mvc\Collection\GridFS

```php
$di->set('collectionManager', function() {
    $modelsManager = new Phalcon\Mvc\Collection\Manager();
    return $modelsManager;
}, true);

$di->set('mongo', function(){
	$m = new MongoClient();
	return $m->selectDB('file');
}, true);

class Images extends \Phalcon\Mvc\Collection\GridFS {
}

$image = new Images;
$image->author = $author;
$image->save($filename);

$image = Images::findFirst();
```