fix update_account_associations for rails 3

Change-Id: I3c119c315cb0224407d1ba3c1ccd26933445fb16
Reviewed-on: https://gerrit.instructure.com/28456
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>