add polyfill

Author: torounit

tests/bootstrap.php

@@ -5,7 +5,7 @@
  * @package custom-post-type-permalinks
  */
 
-require dirname( __DIR__ ) . '/vendor/autoload.php';
+require dirname( __DIR__ ) . '/vendor/yoast/phpunit-polyfills/phpunitpolyfills-autoload.php';
 
 $_tests_dir = getenv( 'WP_TESTS_DIR' );