title: Docker compose won't find $PWD environment variable
body: <p>Here's my docker-compose:</p>
  
  <pre><code>version: '2'
  services:
    couchpotato:
      build:
          context: ./couchpotato
          dockerfile: Dockerfile
      ports:
       - 5050:5050
      volumes:
       - "${PWD}/couchpotato/data:/home/CouchPotato/data/"
       - "${PWD}/couchpotato/config:/home/CouchPotato/config/"
  </code></pre>
  
  <p>When I run it inside the shell, in the directory of the docker-compose.yml, I get:</p>
  
  <pre><code>WARNING: The PWD variable is not set. Defaulting to a blank string.
  </code></pre>
  
  <p>and the compose starts with PWD being empty. </p>
  
  <p>I don't see any error in the file, as seen here: <a href="https://docs.docker.com/compose/environment-variables/" rel="noreferrer">https://docs.docker.com/compose/environment-variables/</a></p>