You can specify which runtime(s) to use in your `composer.json` file. Upon a push, Heroku reads the necessary information from `composer.lock`, if present, and falls back to `composer.json` otherwise.| devcenter.heroku.com
A Dependency Manager for PHP| getcomposer.org
A Dependency Manager for PHP| getcomposer.org
A Dependency Manager for PHP| getcomposer.org