Change effective on 06 November 2018
Ruby v2.6.0 preview3 is now available on Heroku. To run your app using this preview version of Ruby, add the following
ruby directive to your Gemfile:
For more information on Ruby 2.6.0-preview3, you can view the release announcement.
Note: This version of Ruby is not suitable for production applications. However, it can be used to test that your application is ready for the December release of Ruby 2.6.0 and to provide feedback to the Ruby core team.