title: Unsupported config option for services.volumes
body: <p>Trying to setup docker for the first time and I'm running into a problem with volumes. I feel pretty confident that the spacing and formatting in the .yml is correct at this point. </p>
  
  <p>I've tried versions 3, 3.1, 3.2, 3.3 and 3.4. All are getting the same error message (below)</p>
  
  <p>Unsupported config option for services.volumes: 'db2_prod'</p>
  
  <pre><code>version: '3'
  
  services:
     liberty:
       image: liberty:${liberty_tag}
       ports:
         - "${liberty_ip}:9080:9080"
         - "${liberty_ip}:9443:9443"
       restart: always
  
     apache:
       image: webapp:${apache_tag}
       ports:
         - "${apache_ip}:80:80"
         - "${apache_ip}:443:443"
       restart: always
  
     db2:
       image: db2:${db2_tag}
       ports:
         - "${db2_ip}:50000:50000"
       stdin_open: true
       tty: true
       restart: always
       volumes:
         - db2_prod:/database/stagg3
  
     volumes:
       db2_prod:
  </code></pre>