spec: fix roles_api_spec for rails 3

Change-Id: I0bd6f8414e93784bfe05a8ccacdd046458993482
Reviewed-on: https://gerrit.instructure.com/30907
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>