Resolved issue #10

Sisow now doesn't return an invalid sha1 warning anymore.

Author: robinvalk

src/Message/CompletePurchaseRequest.php

@@ -12,7 +12,8 @@ class CompletePurchaseRequest extends PurchaseRequest
     protected function generateSignature()
     {
         return sha1(
-            $this->getTransactionReference() . $this->getMerchantId() . $this->getMerchantKey()
+            $this->getTransactionReference() . $this->getShopId() .
+            $this->getMerchantId() . $this->getMerchantKey()
         );
     }