allow bundler 1.7.4

Change-Id: Ib4f399df45a74a6dcf1ab6d3bedc6bf99f659afc
Reviewed-on: https://gerrit.instructure.com/43374
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Paul Hinze <paulh@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>