fix rails3 specs for rubrics_controller_spec

Change-Id: I5d842aa9dbba5c709eea637b8dc136eab787220f
Reviewed-on: https://gerrit.instructure.com/30172
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Jon Willesen <jonw@instructure.com>
QA-Review: Jon Willesen <jonw@instructure.com>