fix context_modules_controller_spec for rails 3

Change-Id: I453aa576bad33454b669b6efc4810a15ad7bcdd7
Reviewed-on: https://gerrit.instructure.com/29844
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: James Williams  <jamesw@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>