title: How to import npm module having hyphen in name in angular4
body: <p>I want to use <code>array-to-tree</code> npm module in angular4 project. But when I use <code>import { array-to-tree } from 'array-to-tree';</code> it gives error <strong>string leteral expected</strong>.</p>
  
  <p>Please help.</p>