Remove Travis failure exemption for Ruby 2.1.0

This was necessary for a short time because of an issue with Travis'
build environment for Ruby 2.1.0. That has since been fixed, so this can
be removed.

Change-Id: Ib1831e872881a7ade0edd19caaf74408b9049a53
Reviewed-on: http://gerrit.causes.com/39137
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>