payment: fix copyright header in DefaultNoOpGatewayNotification
/*
- * Copyright 2015 Groupon, Inc
- * Copyright 2015 The Billing Project, LLC
+ * Copyright 2015-2018 Groupon, Inc
+ * Copyright 2015-2018 The Billing Project, LLC
*
* The Billing Project licenses this file to you under the Apache License, version 2.0
* (the "License"); you may not use this file except in compliance with the
