fixed older phpunit version

Author: Tommy Quissens

app/code/Magento/Customer/Test/Unit/Model/Checkout/ConfigProviderTest.php

@@ -1,6 +1,6 @@
 <?php
 /**
- * Copyright © Magento, Inc. All rights reserved.
+ * Copyright © 2013-2017 Magento, Inc. All rights reserved.
  * See COPYING.txt for license details.
  */
 namespace Magento\Customer\Test\Unit\Model\Checkout;
@@ -14,7 +14,7 @@
 use Magento\Customer\Model\Form;
 use Magento\Store\Model\ScopeInterface;
 
-class ConfigProviderTest extends \PHPUnit\Framework\TestCase
+class ConfigProviderTest extends \PHPUnit_Framework_TestCase
 {
     /**
      * @var ConfigProvider