ruby 2.5.1, rails 5.1.6, and friends bugfix releases last week.
$ bin/rails s
=> Booting Puma
=> Rails 5.1.6 application starting in development
=> Run `rails server -h` for more startup options
Puma starting in single mode...
* Version 3.11.3 (ruby 2.4.4-p296), codename: Love Song
* Min threads: 5, max threads: 5
* Environment: development