added procfile to make dart to work in heroku - https://devcenter.heroku.com/articles/procfile   Procfile is a mechanism for declaring what commands are run by your application.s dynos on the Heroku platform. It follows the process model on the large scale of the Heroku dyno manifold. You can use a Procfile to declare various process types, such as multiple types of workers, a singleton process like a clock, or a consumer of the Twitter streaming API