fix notification message creator spec for rails 3

Change-Id: Ia16f84249c92d4785379f658be159c73b2677c1e
Reviewed-on: https://gerrit.instructure.com/31334
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>