title: How to get rails master.key after upgrading to rails 5.2
body: <p>So I've upgraded an app I'm working on to rails 5.2 and it's crashing on Heroku. I think it's because I don't have a master.key file in my /config folder. I still have the secrets.yml file from the previous rails version. What do I have to do to resolve this issue?
  Thanks!</p>
  
  <p>error in heroku logs:</p>
  
  <pre><code>2019-01-28T21:07:46.922561+00:00 app[web.1]: /app/vendor/bundle/ruby/2.5.0/gems/aws-sdk-s3-1.30.1/lib/aws-sdk-s3/bucket.rb:684:in `extract_name': Cannot load `Rails.config.active_storage.service`: (ArgumentError)
  2019-01-28T21:07:46.922573+00:00 app[web.1]: missing required option :name
  </code></pre>