title: docker-compose build args not passing to Dockerfile
body: <p>docker-compose.yml:</p>
  
  <pre><code>version: "3"
  
  services:
    ei:
      build:
        context: .
        dockerfile: Dockerfile
        args:
          NODE_VERSION: 8
          HELLO: 5
  </code></pre>
  
  <p>Dockerfile:</p>
  
  <pre><code>ARG NODE_VERSION
  ARG HELLO
  
  FROM node:$NODE_VERSION
  
  RUN echo "-&gt; $HELLO"
  RUN echo "-&gt; $NODE_VERSION"
  </code></pre>
  
  <p>Results in:</p>
  
  <pre><code>km@Karls-MBP ~/dev/ve (km/ref) $ docker-compose -f docker-compose.yml build --no-cache
  vertica uses an image, skipping
  Building ei
  Step 1/14 : ARG NODE_VERSION
  Step 2/14 : ARG HELLO
  Step 3/14 : FROM node:$NODE_VERSION
   ---&gt; e63de54eee16
  Step 4/14 : RUN echo "-&gt; $HELLO"
   ---&gt; Running in e93d89e15913
  -&gt; 
  Removing intermediate container e93d89e15913
   ---&gt; c305b277291c
  Step 5/14 : RUN echo "-&gt; $NODE_VERSION"
   ---&gt; Running in 39e8e656c0bd
  -&gt; 8
  </code></pre>
  
  <p>I'm scratching my head as to why this isn't working. If I change the node version number the number changes.</p>