Added use stdClass in unit test for PHP 7.1 and 7.2 compatibility

Author: ezimuel

util/template/test/unit-test-oss

@@ -18,6 +18,7 @@ namespace :namespace;
 
 use PHPUnit\Framework\TestCase;
 use Elasticsearch\Tests\Utility;
+use stdClass;
 
 /**
  * YAML test for Elasticsearch

util/template/test/unit-test-xpack

@@ -18,6 +18,7 @@ namespace :namespace;
 
 use PHPUnit\Framework\TestCase;
 use Elasticsearch\Tests\Utility;
+use stdClass;
 
 /**
  * YAML test for Elasticsearch