Change effective on 02 August 2018
Heroku now provides early-access versions of JDK 11. To use JDK 11 with your Java, Scala, Clojure, Groovy, or JRuby application, create a
system.properties file in the root directory of your repository with the following contents:
Then add the file to Git, and JDK 11 will be installed the next time you deploy.