fix student_reports_spec for rails 3

Change-Id: Ib9cd7cf32d03c054016bd4babcd6230d7389bbae
Reviewed-on: https://gerrit.instructure.com/31089
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>