Set explicit visibility on MDOutputHandler destructor

src/MDOutputHandler.php

@@ -166,7 +166,8 @@ public function __construct() {
      *
      * @return void
      */
-    function __destruct() {
+    public function __destruct() {
+
         $endtime = \microtime(true);
         $this->toLog("Finished operation. Processing duration: " . \strval($endtime - $this->_startTime));