fix groups_controller_spec for rails 3

Change-Id: Iafbe1ef3a274d3c2c863ff4ca7fbf16cb9d84fcb
Reviewed-on: https://gerrit.instructure.com/29900
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Cody Cutrer <cody@instructure.com>
Product-Review: Landon Wilkins <lwilkins@instructure.com>
QA-Review: Landon Wilkins <lwilkins@instructure.com>