JRuby warns to use a more recent version, but it's blank

[schneems]

This check should not even be firing for a JRuby app. Here's the output:

remote:        Asset precompilation completed (18.27s)
remote:        Cleaning assets
remote:        Running: rake assets:clean
remote: -----> Detecting rails configuration
remote:
remote: ###### WARNING:
remote:
remote:        There is a more recent Ruby version available for you to use:
remote:
remote:
remote:
remote:        The latest version will include security and bug fixes. We always recommend
remote:        running the latest version of your minor release.
remote:
remote:        Please upgrade your Ruby version.
remote:
remote:        For all available Ruby versions see:
remote:          https://devcenter.heroku.com/articles/ruby-support#supported-runtimes