This article outlines how to define a specific version of Ruby for your application.
In your Gemfile you can add the following line:
ruby '2.3.1'
You can find a full listing of Ruby version here. As a recommendation, we always suggest running the latest stable release of Ruby.
Once you've saved changes to your Gemfile, you can push your changes to Datica using git push datica master. The platform will automatically detect the version change.