Require a newer version of "resque-scheduler"

* In an attempt to not get too far behind, bump the "resque-scheduler"
  version to "~> 2.5"

This ensures that the dependencies on scheduler are up to date. I would suggest, if you see fit, merging this, cutting the "1.1.1" gem and yanking version "1.1.0" (its dependencies were too restrictive).