refs DE-523
Previously, the current version would be represented by Gemfile.lock and the next version by Gemfile.lock.next. Replace both with a common format of Gemfile.rails<version>.lock to be able to iterate over the files in a cleaner way.
Change-Id: I35aef3a14e726eb35db8aebc808af4a925552c01
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/288563
Tested-by: Service Cloud Jenkins <svc.cloudjenkins@instructure.com>
Reviewed-by: Jacob Burroughs <jburroughs@instructure.com>
QA-Review: Aaron Ogata <aogata@instructure.com>
Product-Review: Aaron Ogata <aogata@instructure.com>