fix calendar events controller spec for rails 3

Change-Id: I70d15336115a118f4d36bf7fa3b0bc2b4f49bf6b
Reviewed-on: https://gerrit.instructure.com/29798
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>