title: How to make workbox cache cross origin responses?
body: <p>According to <a href="https://developers.google.com/web/tools/workbox/modules/workbox-routing" rel="noreferrer">workbox doc</a>, cross domain request should be configured  to ensure that regular expression matches the beginning of the URL. However, it doesn't work.</p>
  
  <p>The service worker code is like below.</p>
  
  <pre><code>importScripts('https://storage.googleapis.com/workbox-cdn/releases/3.0.0/workbox-sw.js');
  
  workbox.routing.registerRoute(
    /.*\.(png|jpg|jpeg|svg|gif)/,
    workbox.strategies.cacheFirst()
  );
  
  workbox.routing.registerRoute(
    new RegExp('^https://a248.e.akamai.net/.*'),
    workbox.strategies.cacheFirst()
  );
  </code></pre>
  
  <p>In the page, responses from same origin resources are cached, but responses from <code>https://a248.e.akami.net</code> is not. </p>
  
  <p>Anything wrong with my config? or is this a workbox 3.0.0 bug?</p>