Added Payment Express / DPS (A2A)

Author: onlinesid

README.md

@@ -157,6 +157,7 @@ Gateway | Composer Package | Maintainer
 [PayFast](https://github.com/thephpleague/omnipay-payfast) | omnipay/payfast | [Omnipay](https://github.com/thephpleague/omnipay)
 [Payflow](https://github.com/thephpleague/omnipay-payflow) | omnipay/payflow | [Del](https://github.com/delatbabel)
 [PaymentExpress (DPS)](https://github.com/thephpleague/omnipay-paymentexpress) | omnipay/paymentexpress | [Del](https://github.com/delatbabel)
+[PaymentExpress / DPS (A2A)](https://github.com/onlinesid/omnipay-paymentexpress-a2a) | onlinesid/omnipay-paymentexpress-a2a | [Sid](https://github.com/onlinesid)
 [PaymentgateRu](https://github.com/pinguinjkeke/omnipay-paymentgateru) | pinguinjkeke/omnipay-paymentgateru | [Alexander Avakov](https://github.com/pinguinjkeke)
 [PaymentSense](https://github.com/digitickets/omnipay-paymentsense) | digitickets/omnipay-paymentsense | [DigiTickets](https://github.com/digitickets)
 [PaymentWall](https://github.com/incube8/omnipay-paymentwall) | incube8/omnipay-paymentwall | [Del](https://github.com/delatbabel)