title: docker services.web.working_dir contains an invalid type, it should be a string
body: <p>I am trying to up phpserver via docker-compose.
  I put 3 files in my working directory.</p>
  
  <p>.env
  docker-compose.yml
  Dockerfile</p>
  
  <p>.env</p>
  
  <pre><code>##PATHS
  
  DB_PATH_HOST=./databases
  APP_PATH_HOST=./blog
  APP_PATH_CONTAINER=/var/www/html/
  MYSQL_ROOT_PASSWORD=123456
  </code></pre>
  
  <p>docker-compose.yml</p>
  
  <p>version: '3'</p>
  
  <pre><code>services:
    web:
      build: .
      environment:
        - APACHE_RUN_USER=www-data
      volumes:
        - ${APP_PATH_HOST}: ${APP_PATH_CONTAINER}
      ports:
        - 8080:80
      working_dir:
        - ${APP_PATH_CONTAINER}
    db:
      image: mariadb
      restart: always
      environment:
        MYSQL_ROOT_PASSWORD: ${MYSQL_ROOT_PASSWORD}
      volumes:
        - ${DB_PATH_HOST}: /var/lib/mysql
  
    adminer:
      image: adminer
      restart: always
      ports:
        - 6080:8080
    composer:
      image: composer:1.7
      volumes:
        - ${APP_PATH_HOST}: ${APP_PATH_CONTAINER}
      working_dir: ${APP_PATH_CONTAINER}
      command: composer install
  </code></pre>
  
  <p>and Dockerfile</p>
  
  <pre><code>FROM php:7.2-apache
  
  RUN docker-php-ext-install \
       pdo_mysql \
       &amp;&amp; a2enmod
       rewrite
  </code></pre>
  
  <hr>
  
  <p>But after I try to run</p>
  
  <pre><code>docker-compose up --build
  </code></pre>
  
  <p>I have the problem</p>
  
  <pre><code>ERROR: The Compose file '.\docker-compose.yml' is invalid because:
  services.web.working_dir contains an invalid type, it should be a string
  services.composer.volumes contains an invalid type, it should be a string
  services.web.volumes contains an invalid type, it should be a string
  services.db.volumes contains an invalid type, it should be a string
  </code></pre>
  
  <p>I tried to change docker-compose file version  to 2  - does not work
  I tried to use '' and "" the same problem.</p>
  
  <p>I want to run my server successfully.</p>