allow latest bundler

Change-Id: I5a4faf0147442714c4684b259b0ef8241df00155
Reviewed-on: https://gerrit.instructure.com/40631
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>