Ruby apps now default to Node version 10.14.1 and Yarn version 1.12.3

Change effective on 03 January 2019

Applications using the heroku/ruby buildpack that do not have a version of Node installed by another buildpack (such as the heroku/nodejs buildpack) will now receive Node version 10.14.1 and Yarn version 1.12.3.

These versions and instructions on how to specify a specific version of these binaries can be found on the installed binaries section of the Heroku Ruby Support page.