Fix old reference to thirdparty directory

The previous commit moved the composer.json together with the vendor
directory to the root of the repository. Therefore we need to update
the location of Composer’s autoload.php.

Author: dlmsr

classes/output_image.php

@@ -36,7 +36,7 @@
 
 defined('MOODLE_INTERNAL') || die();
 
-require_once($CFG->dirroot . '/blocks/qrcode/thirdparty/vendor/autoload.php');
+require_once($CFG->dirroot . '/blocks/qrcode/vendor/autoload.php');
 require_once($CFG->dirroot . '/course/lib.php');
 
 /**