title: Match multiple file extensions in npm script
body: <p>I have an npm script where I want to match both <code>ts</code> and <code>tsx</code> file extensions... something like below:</p>
  
  <pre><code>"test": "mocha ..... app/test/**/*.spec.{ts,tsx}"
  </code></pre>
  
  <p>However, the above syntax doesn't work.  What's the correct syntax for doing this?</p>