fix update_account_associations for rails 3

Change-Id: I7e0e9db5d4d8f920ce63c4dfcac966783473c39a
Reviewed-on: https://gerrit.instructure.com/29716
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>