Update caching library to latest version, updated and fixed phpUnit tests

tests/OfflineTests/AccountGateway/AccountContextParseTest.php

@@ -9,7 +9,7 @@ namespace CloudObjects\SDK\AccountGateway;
 use GuzzleHttp\Psr7\Request as GuzzlePsrRequest;
 use Symfony\Component\HttpFoundation\Request as SymfonyRequest;
 
-class AccountContextParseTest extends \PHPUnit_Framework_TestCase {
+class AccountContextParseTest extends \PHPUnit\Framework\TestCase {
 
     public function testParsePsrRequest() {
         $request = new GuzzlePsrRequest('GET', '/', [