Add sent-at time to notification payload

lib/server/loop.js

@@ -112,8 +112,12 @@ function init (env, ctx) {
       alert += " - " + data.enteredBy
     }
 
+    // Track time notification was sent
+    let now = new Date()
+    payload['sent-at'] = now.toISOString();
+
     // Expire after 5 minutes.
-    let expiration = new Date((new Date()).getTime() + 5 * 60 * 1000)
+    let expiration = new Date(now.getTime() + 5 * 60 * 1000)
     payload['expiration'] = expiration.toISOString();
 
     let notification = new apn.Notification();