Fixing build.

piwik.php

@@ -15,7 +15,7 @@ use Piwik\Tracker;
 $GLOBALS['PIWIK_TRACKER_DEBUG_FORCE_SCHEDULED_TASKS'] = false;
 define('PIWIK_ENABLE_TRACKING', true);
 
-if (!defined(PIWIK_DOCUMENT_ROOT)) {
+if (!defined('PIWIK_DOCUMENT_ROOT')) {
     define('PIWIK_DOCUMENT_ROOT', dirname(__FILE__) == '/' ? '' : dirname(__FILE__));
 }