Function addorder mistake

[karik741]

public function addOrder($currency, $amount, $rate = null, $params = []) {
         $optional['symbol'] = $currency; // NOT OPTIONAL - $PARAMS
         $optional['quantity'] = $amount;  // NOT OPTIONAL - $PARAMS
         if (empty($params['type'])) $params['type'] = 'market';
         if (!empty($rate)) $params['price'] = $rate;

         return $this->request('order', $optional['clientOrderId'] ? 'order/' . $optional['clientOrderId'] : null, $params, 'POST');
    }

[dzarezenko]

Hi,
if you have some suggestions on code improvements or bug fixes - make pull request please.