test: fix test error

src/service-worker.js

@@ -55,12 +55,10 @@ addEventListener('message', event => {
   const message = event.data;
   if (replyPort && message && message.type === 'skip-waiting') {
     event.waitUntil(
-      self
+      self.skipWaiting().then(
-        .skipWaiting()
+        () => replyPort.postMessage({ error: null }),
-        .then(
+        error => replyPort.postMessage({ error }),
-          () => replyPort.postMessage({ error: null }),
+      ),
-          error => replyPort.postMessage({ error }),
-        ),
     );
   }
 });