spec: fix filter_chain manipulation for rails 3

Change-Id: I3a23c8e7e1fd2ac26073eee1d8595303e6508312
Reviewed-on: https://gerrit.instructure.com/30690
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>