add script for fetching HEAD revision from heroku
add script for fetching HEAD revision from heroku

perobertson/shipit-engine,Shopify/shipit-engine,ershad/shipit-engine,Shopify/shipit-engine,ershad/shipit-engine,ershad/shipit-engine,Shopify/shipit-engine,perobertson/shipit-engine,Shopify/shipit-engine,perobertson/shipit-engine,ershad/shipit-engine,ershad/shipit-engine,Shopify/shipit-engine,perobertson/shipit-engine,perobertson/shipit-engine