Change effective on 25 April 2019
The Heroku Node buildpack will no longer support deploying using io.js as an alternative runtime.
io.js was a fork of the Node runtime that was merged back into the Node.js project in 2015. It has been unsupported for several years and is likely to contain several large security vulnerabilities that have been patched in Node.js.
Any users still using io.js to deploy are encouraged to upgrade to a supported version of Node.js.