fix date in_time_zone extension for rails 3

Change-Id: Iea25c198656e30053a722f65109c8e028af54a25
Reviewed-on: https://gerrit.instructure.com/28692
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: James Williams  <jamesw@instructure.com>
Product-Review: James Williams  <jamesw@instructure.com>