Wrong image path on tutorial page

[kenorb]

Path: /booking/admin/config/booking_timeslots/tutorial
File: /templates/tutorial.tpl.php

E.g.

<img src="/<?php print $dir; ?>/images/tutorial_opening_hours_non_venue.png" style="border: 0;" />

when $dir = drupal_get_path('module', 'booking_timeslots');

which calculates the wrong webroot path when website is using URI prefix (e.g. http://example.com/prefix/).