title: docker compose file not working: replicas Additional property replicas is not allowed
body: <p>docker version: 17.03.1-ce</p>
  
  <p>Trying to get the docker-compose.yml working from the getting started tutorials.</p>
  
  <pre><code>version: "3"
     services:
       web:
         image: tuhina/friendlyhello:2.0
       deploy:
         replicas: 5
         resources:
           limits:
             cpus: "0.1"
             memory: 50M
        restart_policy:
          condition: on-failure
        ports:
          - "80:80"
        networks:
          - webnet
      networks:
        webnet:
  </code></pre>
  
  <p>Getting this error:</p>
  
  <pre><code>replicas Additional property replicas is not allowed
  </code></pre>
  
  <p>What have I typed in wrong?</p>
  
  <p>Thanks.</p>
  
  <p>edit: docker-compose version 1.11.2, build dfed245</p>