Fix regular time check

We used setTimeout instead of setInterval, so the periodic check was
only performed twice.

Change-Id: I62732483c3d412f1690d01de4a25cdb8249db494
diff --git a/sw.js b/sw.js
index d70baaf..023c2e2 100644
--- a/sw.js
+++ b/sw.js
@@ -1,4 +1,4 @@
-// Version: 1.0.1
+// Version: 1.0.2
 var CACHE_NAME = 'all-v1';
 var urlsToCache = [
   '/',