title: Separate secret_key_base in Rails 5.2?
body: <p>I just upgraded from 5.1 to 5.2 and I'm quite confused about this 'better' methodology to storing secrets...</p>
  
  <p>Maybe I'm not understanding, but it seems like now development and production have been 'merged' into a SINGLE <code>SECRET_KEY_BASE</code> as well as <code>master.key</code>... is this correct?</p>
  
  <p>If not, how do I use a separate master key and <code>SECRET_KEY_BASE</code> in development?</p>
  
  <p>What if I have developers helping me and I don't want them to know my master key (or secrets) I use in production?</p>