Added new relic in production

I'm not sure if anything else needs to be done based on this line in the new relic documentation: 
https://newrelic.com/docs/ruby/sinatra-support-in-the-ruby-agent
The New Relic Ruby agent will not work with shotgun. It cannot make a connection before the dispatcher process exits. Neither developer mode nor monitor mode will work. 

I've already set the RACK_ENV variable in heroku to 'production'.