fix rake for rspec2

Change-Id: I4343e245f392d440746a7cef3060dd07b59f86cf
Reviewed-on: https://gerrit.instructure.com/29073
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>