title: Docker stack deploy error about top-level object mappings
body: <p>Following along with the Docker getting started guide, <a href="https://docs.docker.com/get-started/part3/#your-first-docker-composeyml-file" rel="noreferrer">https://docs.docker.com/get-started/part3/#your-first-docker-composeyml-file</a>, I'm running into an issue. I've created the docker-compose.yml file and verified that the contents are correct:</p>
  
  <pre><code>version: "3"
  services:
    web:
      image: joshuabelden/get-started:part2
      deploy:
        replicas: 5
        resources:
          limits:
            cpus: "0.1"
            memory: 50M
        restart_policy:
          condition: on-failure
      ports:
        - "80:80"
      networks:
        - webnet
  networks:
    webnet:
  </code></pre>
  
  <p>I also verified that I can run my image outside of a swarm. After running the command:</p>
  
  <pre><code> docker stack deploy -c docker-compose.yml getstartedlab
  </code></pre>
  
  <p>I'm getting the following error:</p>
  
  <pre><code>Top-level object must be a mapping
  </code></pre>
  
  <p>I can't seem to find any information on the error message.</p>