remove deprecation warning in ruby 2.1

Change-Id: I458ba8a1dc0d399d4a127712addf7f310994d098
Reviewed-on: https://gerrit.instructure.com/36726
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Rob Orton <rob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>