title: docker-compose 1.6 "args" attribute on "build"
body: <p>I'm trying to use the new "args" attribute to pass variable to Dockerfile build. But the yaml parser is not accepting the parameter.</p>
  
  <pre><code>ERROR: yaml.scanner.ScannerError: mapping values are not allowed here
  </code></pre>
  
  <p>For version 2 of docker-compose.yml the requirements are docker-compose 1.6+ and docker-engine 1.10+ and I have both them installed. </p>
  
  <p>This is part of my docker-compose file:</p>
  
  <pre><code>version: '2'
  services:
   solr:
      build: ./solr
        args:
          solr_port: 8983
      volumes:
        - ./apps/solr-conf:/opt/solr/server/solr
      ports:
        - 8983:8983
  </code></pre>
  
  <p>The error refers to the "args" line. </p>