title: How to set RAILS_PRODUCTION_KEY config var on a Rails 6 app on Heroku
body: <p>I created a new Rails 6 app and since it supports Multi Environment Credentials I'm trying to use the <code>RAILS_PRODUCTION_KEY</code> config var and delete the default <code>RAILS_MASTER_KEY</code></p>
  <pre><code>heroku config:unset RAILS_MASTER_KEY 
  heroku config:set RAILS_PRODUCTION_KEY=`cat config/credentials/production.key`
  </code></pre>
  <p>This doesn't work however, and I was able to get it to work after setting <code>RAILS_MASTER_KEY</code> to the production key</p>
  <pre><code>heroku config:unset RAILS_PRODUCTION_KEY
  heroku config:set RAILS_MASTER_KEY=`cat config/credentials/production.key`
  </code></pre>
  <p>How do I get Heroku to recognize <code>RAILS_PRODUCTION_KEY</code> in a Rails 6 app?</p>