Add getTransactionId function.

eWay has a function to retrieve the merchant (originating website) generated
ID but it should implement the standardised Omnipay one per

https://github.com/thephpleague/omnipay#successful-response

which is ->getTransactionId(); // the reference set by the originating website if available.

Author: eileenmcnaughton

src/Message/RapidResponse.php

@@ -63,8 +63,23 @@ public function getCardReference()
         return null;
     }
 
+    /**
+     * Get the transaction ID as generated by the merchant website.
+     *
+     * @return string
+     */
+    public function getTransactionId()
+    {
+        return $this->data['InvoiceNumber'];
+    }
+
     /**
      * Get InvoiceNumber - merchant reference for a transaction
+     *
+     * @deprecated Omnipay standard interface is to return this when getTransactionId
+     * is called
+     *
+     * @see https://github.com/thephpleague/omnipay#successful-response
      */
     public function getInvoiceNumber()
     {