Add require_once to update.php due to routing

Fixes https://github.com/owncloud/core/issues/10585
Partially reverts 52d5429768

core/ajax/update.php

@@ -1,5 +1,6 @@
 <?php
 set_time_limit(0);
+require_once '../../lib/base.php';
 
 if (OC::checkUpgrade(false)) {
 	$l = new \OC_L10N('core');