old_contents: import React from 'react';
  import ReactDOM from 'react-dom';
  import './index.css';
  import App from './App';
  import registerServiceWorker from './registerServiceWorker';
  
  ReactDOM.render(<App />, document.getElementById('root'));
  registerServiceWorker();
  
new_contents: import React from 'react';
  import ReactDOM from 'react-dom';
  import './index.css';
  import App from './App';
  // import registerServiceWorker from './registerServiceWorker';
  
  ReactDOM.render(<App />, document.getElementById('root'));
  // registerServiceWorker();
  
subject: Disable service worker