Ensure that all pending intents have the IMMUTABLE tag

Per https://developer.android.com/guide/components/intents-filters#CreateImmutablePendingIntents

> In most cases, your app should create immutable PendingIntent objects, as
> shown in the following code snippet. If a PendingIntent object is immutable,
> then other apps cannot modify the intent to adjust the result of invoking the
> intent.

Our usage here falls into this common case, so we can just make them be immutable

src/android/NotificationHelper.java

@@ -51,7 +51,7 @@ public static void createNotification(Context context, int id, String title, Str
 		activityIntent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
 
 		PendingIntent activityPendingIntent = PendingIntent.getActivity(context, 0,
-				activityIntent, PendingIntent.FLAG_UPDATE_CURRENT);
+				activityIntent, PendingIntent.FLAG_UPDATE_CURRENT | PendingIntent.FLAG_IMMUTABLE);
 		builder.setContentIntent(activityPendingIntent);		
 
 		Log.d(context, TAG, "Generating notify with id " + id + " and message " + message);
@@ -85,7 +85,7 @@ public static void createResolveNotification(Context context, int id, String tit
 		activityIntent.putExtra(NotificationHelper.RESOLUTION_PENDING_INTENT_KEY, intent);
 
 		PendingIntent activityPendingIntent = PendingIntent.getActivity(context, 0,
-				activityIntent, PendingIntent.FLAG_UPDATE_CURRENT);
+				activityIntent, PendingIntent.FLAG_UPDATE_CURRENT | PendingIntent.FLAG_IMMUTABLE);
 		builder.setContentIntent(activityPendingIntent);
 		// builder.setAutoCancel(true);