fixed dead-letter-queue feature

The second argument to [`basic_reject()`](https://github.com/videlalvaro/php-amqplib/blob/master/PhpAmqpLib/Channel/AMQPChannel.php#L682) was missing.

See http://www.rabbitmq.com/blog/2010/08/03/well-ill-let-you-go-basicreject-in-rabbitmq/