change bullet gem in test.rb

Change-Id: Ida59b503ba4230bdb93581b5d9d9c0ad28b4faf0
Reviewed-on: https://gerrit.instructure.com/30064
Reviewed-by: Kyle Rosenbaum <kyler@instructure.com>
Product-Review: Kyle Rosenbaum <kyler@instructure.com>
QA-Review: Kyle Rosenbaum <kyler@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>