title: "config should have required property 'media_folder'" - when it does
body: <p>Its been a while since I've played with netlifycms - and I feel I've had this problem before but can't find the answer. My config.yml has the media_folder in it - but I'm getting an error it can't find a config setting for one - anyone have any ideas? So this is my config (<a href="https://github.com/AceCentre/nhs-service-finder/blob/master/static/admin/config.yml" rel="nofollow noreferrer">full file</a></p>
  
  <pre><code>backend:
    name: github
    repo: acecentre/nhs-service-finder
    branch: master 
  
  collections:
    - name: "nhs-service" 
      label: "Service" 
      folder: "content/ccg" 
      media_folder: "static/images/uploads"
      media_library:
        name: uploads    
      create: false 
  </code></pre>
  
  <p>But on loading the page (<a href="https://servicefinder.acecentre.net/admin/" rel="nofollow noreferrer">here</a>) I get </p>
  
  <pre><code>Config Errors:
  config should have required property 'media_folder'
  config should have required property 'media_library'
  config should match some schema in anyOf
  Check your config.yml file.
  </code></pre>
  
  <p>What am I doing wrong?</p>