Update state_machines-activerecord from 0.3.0 to 0.4.0.
Upgrade state_machines-activerecord gem from 0.3.0 to 0.4.0.
No changelog, see commits: https://github.com/state-machines/state_machines-activerecord/commits/master
Includes support for Rails 5, working towards #14286 (moved).
cc: @rspeicher