Support for Rails4 and Ruby2.1

Added support for rails 4 and ruby 2.1. Using the latest version of the `casino` gem.

 I removed `verify_active_connections` because it is obsolete nowadays. See https://github.com/rails/rails/commit/9d1f1b1ea9e5d637984fda4f276db77ffd1dbdcb for more details.