title: Getting 'ERROR in ./src/polyfills.ts' while running `ng build --prod`
body: <p>I have setup Angular 6 project. 
  I am trying to run <code>ng build --prod</code> but I am getting below error </p>
  
  <blockquote>
    <p>Module not found: Error: Can't resolve 'core-js/es7/reflect' in 'c:\localpath'</p>
  </blockquote>
  
  <p>I am getting this error Angular 6 CLI version.</p>