title: Prevent skip in docker-compose
body: <p>I have a <code>docker-compose.yml</code> for a Django web app with a backend. It looks like this:</p>
  
  <pre><code>version: '2'
  
  services:
    db:
      image: # special image
      ports:
        - "1433:1433"
      environment:
        PASSWORD: "*********"
  
    web:
      build: .
      command: python manage.py runserver 0.0.0.0:8000
      ports:
        - "8000:8000"
      depends_on:
        - db
  </code></pre>
  
  <p>When I run <code>sudo docker-compose build</code>, the first line of output says </p>
  
  <pre><code>db uses an image, skipping. 
  Building web.
  </code></pre>
  
  <p>I need the <code>db</code> image to be built before <code>web</code>. </p>
  
  <p>How can I make the <code>db</code> image get built first?</p>