title: Run Redis with persistent storage using docker-compose
body: <p>How do I tell CircleCI and docker-compose to run Redis with persistent storage? I expected to see something like <code>docker run -d -p 6379:6379--name redis dockerfile/redis</code> in circle.yml where I can add a <code>-v &lt;data-dir&gt;:/data</code> to, but I only see <code>redis</code> listed under <code>services:</code> in circle.yml:</p>
  
  <pre><code>machine:
    services:
      - redis
    node:
      version: 6.3.0
    python:
      version: 3.5.2
  
  # ...deployment commands follow, but no redis
  </code></pre>