Use PHPUnit\Framework\TestCase instead of PHPUnit_Framework_TestCase

tests/PayPal/Test/Api/AddressTest.php

@@ -1,15 +1,15 @@
 <?php
-
 namespace PayPal\Test\Api;
 
 use PayPal\Api\Address;
+use PHPUnit\Framework\TestCase;
 
 /**
  * Class Address
  *
  * @package PayPal\Test\Api
  */
-class AddressTest extends \PHPUnit_Framework_TestCase
+class AddressTest extends TestCase
 {
     /**
      * Gets Json String of Object Address
@@ -29,7 +29,6 @@ class AddressTest extends \PHPUnit_Framework_TestCase
         return new Address(self::getJson());
     }
 
-
     /**
      * Tests for Serialization and Deserialization Issues
      * @return Address