Update eventsIndex.php

We don't use media_duration, we use video_duration!

PHP message: PHP Notice:  Undefined index: media_duration in /usr/share/bluecherry/www/ajax/events/eventsIndex.php on line 128

root@fvi-bcdvr1:/usr/share/bluecherry/www/ajax/events# grep "media_duration" /var/log/nginx/bluecherry-error.log |wc -l
243107

www/ajax/events/eventsIndex.php

@@ -125,7 +125,7 @@ public function getData()
                     $entry['content'] = array(
                         'media_id' => $item['media_id'],
                         'media_size' => $item['media_size'],
-                        'media_duration' => $item['media_duration'],
+                        'media_duration' => $item['video_duration'],
                         'content' => (!empty($_SERVER['HTTPS']) ? 'https' : 'http') . '://' . $_SERVER['HTTP_HOST'] . '/media/request.php?id=' . $item['media_id']
                     );
                 }