allow bundler 1.5.3

Change-Id: I279baaf8304b153c7d16e9e0c798c6426ca03898
Reviewed-on: https://gerrit.instructure.com/30036
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Brian Palmer <brianp@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>