self.addEventListener('install', event => {
  event.waitUntil(
    fetch(createCacheBustedRequest(OFFLINE_URL)).then(function(response) {
      return caches.open(CURRENT_CACHES.offline).then(function(cache) {
        return cache.put(OFFLINE_URL, response);
      }).then(function () {
      	updateStaticCache();
      });
    })
  );
});