fix for discussion_entries_controller for rails 3

Change-Id: Ib1ac230cefdc984d6709893ea47278f793037369
Reviewed-on: https://gerrit.instructure.com/29963
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>