allow bundler 1.5.2

Change-Id: I923aadfba23d416efa788a4a5d2519ea9b960dbc
Reviewed-on: https://gerrit.instructure.com/28594
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Nick Cloward <ncloward@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>