title: ERROR: Version in "./docker-compose.yml" is unsupported
body: <p>I am running docker-compose build in a folder with the relevant docker files and yml files. I see the following error</p>
  
  <pre><code>root@ubuntu187_demo_2:~/IDOLDockerContainers_12.4.0_COMMON/basic-idol# docker-compose build
  ERROR: Version in "./docker-compose.yml" is unsupported. You might be seeing this error because you're using the wrong Compose file version. Either specify a supported version (e.g "2.2" or "3.3") and place your service definitions under the `services` key, or omit the `version` key and place your service definitions at the root of the file to use version 1.
  For more on the Compose file format versions, see https://docs.docker.com/compose/compose-file/
  </code></pre>
  
  <p>The docker-compose.yml is as follows</p>
  
  <pre><code># Basic IDOL container setup
  # Uses nifi to ingest and index data into content
  # Uses find to make search results available
  # Default admin user is created for find in the community service
  #  - see community/run_community.sh for details
  
  version: "3.7"
  
  x-args-shared:
    - &amp;idol-version IDOL_VERSION=12.4.0 # version of IDOL components to use
  
  # Change the IP to the address of an external IDOL LicenseServer instance
  x-external-licenseserver-host: &amp;external-licenseserver-host
    - "idol-licenseserver:xx.xx.xx.xx"
  
  # Shared volume configuration for nifi and view service - see volumes
  x-idol-ingest-volume: &amp;idol-ingest-volume
    - idol-ingest-volume:/idol-ingest
  
  #x-idol-categorisation-volume: &amp;idol-categorisation-volume
  #  - idol-categorisation-volume:/idol-categorisation
  
  # Shared volume in NiFi and View
  # Any files dropped into this volume will be ingested and indexed
  volumes:
    idol-ingest-volume:
  # idol-categorisation-volume:
  
  services:
    idol-content:
      image: idol-compose/content
      build:
        context: ./content
        args:
          - *idol-version
      extra_hosts: *external-licenseserver-host
      ports:
        - 9100:9100
  </code></pre>
  
  <p>docker-compose version</p>
  
  <pre><code>root@ubuntu18_demo_2:~/IDOLDockerContainers_12.4.0_COMMON/basic-idol# docker-compose -version
  docker-compose version 1.17.1, build unknown
  </code></pre>
  
  <p>docker version</p>
  
  <pre><code>root@ubuntu18_demo_2:~/IDOLDockerContainers_12.4.0_COMMON/basic-idol# docker -v
  Docker version 19.03.1, build 74b1e89
  </code></pre>
  
  <p>I can't change the version on the docker-compose.yml file. </p>