Author: rwijaya
MDL-42338 lti_mod: convert hardcoded string.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=45535d95b3e6ce1a18375a9b6eb7d7c16fe704d0
http://github.com/moodle/moodle/commit/45535d95b3e6ce1a18375a9b6eb7d7c16fe704d0
+ 2.6 en [submissionsfor,mod_lti]