Fix comma in app.json.
Fix comma in app.json.

jgao1995/TextFeed,TwilioDevEd/clicktocall-flask,TwilioDevEd/clicktocall-flask,RobSpectre/Twilio-Hackpack-for-Heroku-and-Flask,RobSpectre/Mustached-Message-Service,RobSpectre/Twilio-Hackpack-for-Heroku-and-Flask,ryin1/textfeed,jgao1995/TextFeed,TwilioDevEd/clicktocall-flask