title: How can I build the dev env and the prod env differently in build time? etc) db config
body: <p>i am using create-react-app, i should set the project prod env, dev env diffrently and deploy to dev server &amp; prod server(seperated)</p>
  
  <p>in now, i cant found the good way about this issue, i am changing myself config value before deploy to server(prod or dev). but it is 
  inefficient and unstable.</p>
  
  <p>for example)</p>
  
  <p>//config.json</p>
  
  <pre><code>...
  "db": {
      "prodSchema": "foo_p",
      "devSchema": "foo_d",
      "username": "dany",
      "password": "****",
      "host": "123.456.789.111:3306",
      "dialect": "mysql"
  },
  ...
  </code></pre>
  
  <p>and use</p>
  
  <p>//config use.js</p>
  
  <p>in deploy, check &amp; change...</p>
  
  <pre><code>//db.connect(config.prodSchema)
  db.connect(config.devSchema)
  </code></pre>
  
  <p>i want get set way before 'yarn build' prod env &amp; dev env differently in create-react-app</p>