[Python] H14 error in heroku - "no web processes running"

error H14 happen while deploying to heroku this is my procfile:

web: gunicorn -w 4 -b 0.0.0.0:$PORT -k gevent main:app


log on heroku:

2017-01-23T10:42:58.904480+00:00 heroku[router]: at=error code=H14 desc="No web processes running" method=GET path="/" host=meetcapstone.herokuapp.com request_id=df88efb5-a81a-4ac0-86dc-4e03d71266bb fwd="81.218.117.137" dyno= connect= service= status=503 bytes=
2017-01-23T10:42:59.009135+00:00 heroku[router]: at=error code=H14 desc="No web processes running" method=GET path="/favicon.ico" host=meetcapstone.herokuapp.com request_id=21cea981-36b0-4410-891f-548bbc29f0ee fwd="81.218.117.137" dyno= connect= service= status=503 bytes=


requirements:

Flask==0.11.1
passlib==1.7.0
SQLAlchemy==1.1.5
Werkzeug==0.11.15
gunicorn==19.0.0
gevent==1.2.1

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