Typo in FirebaseUtil.java

[MichaelsPlayground]

Dear Bimal,

First of all - thank you for this fine piece of code, it helps me a lot in setting up an own Firebase chatting app.

When testing your code I found a typo in FirebaseUtils.java:

In timestampToString you are formatting a timestamp to a short string with an "oneliner":
return new SimpleDateFormat("HH:MM").format(timestamp.toDate());
but this will return the hour and Month of the timestamp. Better use this:
return new SimpleDateFormat("HH:mm").format(timestamp.toDate());
to return the hour and minute of the timestamp.

B.t.w.: you should note in your description that the Notification Service is just a stub and not a working feature. I added the necessary files by using the sample file in "https://github.com/firebase/quickstart-android/blob/master/messaging/app/src/main/java/com/google/firebase/quickstart/fcm/java/MyFirebaseMessagingService.java".

Greetings
Michael