rails3: fix failing assignment spec

Change-Id: I0dac49406c087e1877b02d7201c7095c5bd2a099
Reviewed-on: https://gerrit.instructure.com/30894
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
Product-Review: Cameron Matheson <cameron@instructure.com>
QA-Review: Cameron Matheson <cameron@instructure.com>