title: Docker compose doesn't recognize 'env_file'
body: <p>I am trying to run <code>docker-compose up</code> with the following configuration:</p>
  
  <pre class="lang-yaml prettyprint-override"><code>php:
      image: php:7.0-fpm
      expose:
          - 9000
      links:
          - nginx
  
  nginx:
      env_file: .env
      image: nginx:latest
      ports:
          - 80:80
          - 433:433
      environment:
          - NGINX_HOST: ${APP_URL}
  
  mysql:
      env_file: .env
      image: mysql:latest
      ports:
          - 3306:3306
      environment:
          - MYSQL_ROOT_PASSWORD: ${DB_PASSWORD}
          - MYSQL_DATABASE: ${DB_DATABASE}
          - MYSQL_USER: ${DB_USERNAME}
          - MYSQL_PASSWORD: ${DB_PASSWORD}
          - MYSQL_ALLOW_EMPTY_PASSWORD: no
  </code></pre>
  
  <p>I have an <code>.env</code> file in the same directory and am able to test the variable in the shell, but docker doesn't seem to load the <code>.env</code>.</p>
  
  <blockquote>
    <p><strong>WARNING</strong>: The APP_URL variable is not set. Defaulting to a blank string.</p>
    
    <p><strong>WARNING</strong>: The DB_PASSWORD variable is not set. Defaulting to a blank string.</p>
    
    <p><strong>WARNING</strong>: The DB_DATABASE variable is not set. Defaulting to a blank string.</p>
    
    <p><strong>WARNING</strong>: The DB_USERNAME variable is not set. Defaulting to a blank string.</p>
    
    <p><strong>ERROR</strong>: Validation failed in file './docker-compose.yaml'</p>
  </blockquote>
  
  <p><br>
  <strong>UPDATE</strong></p>
  
  <p>I just changed the <code>env_file</code> value to point to a non-existing file and no errors are thrown. It seems like docker is completely ignoring the option.</p>