fix delayed_job before_save callback for rails 3

Change-Id: I0cbd7e32700df6df7cde4c7911fcc9403ae40a5b
Reviewed-on: https://gerrit.instructure.com/29039
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>