Author: Simey Lameze
MDL-59910 core_calendar: add missing typegradingdue lang string
http://git.moodle.org/gw?p=moodle.git;a=commit;h=59641f4eb9c69fd5fbe365b08607bffbacfe8e06
http://github.com/moodle/moodle/commit/59641f4eb9c69fd5fbe365b08607bffbacfe8e06
+ 3.4 en [typegradingdue,core_calendar]