add an heroku target.

to clean, build and connect
add bower as a dependency, and 'bower install' as npm postinstall

not very nice to add bower to dependancy, but it will allow to easily 'bower install' on heroku

a nicer way would be to create a dedicated heroku buildpack.
move grunt related devDependencies to dependencies

grunt is use by heroku to build the app before serving it and heroku only 'npm install --production'
Use of express to serve the application in production mode via Procfile

add express as a dependency
the server now listen on all interfaces, not only localhost
use environment variable $PORT to set the port to listen to.