Replace the filename "image..." of the attached png

-- HikaShop version -- : 3.2.0
-- HikaSerial version -- : 2.0.0
-- Joomla version -- : 3.8.1
-- PHP version -- : 7

Hi,

I am selling vouchers - they are sent to the recipient as attachments (png) with email.

I would like to replace the filename "image..." with a more senseful name like "Voucher_".

I found on line 317 in the plugin/attachserial.php

$filename = 'image'.uniqid().'.'.$extension;