apps: update ts in code instead of database

ts is useful as a versioning mechanism (for example, icon changed). update the timestamp explicity in code instead of db.
this way health and healthTime can be updated without changing ts.

src/appdb.js

@@ -367,6 +367,9 @@ function clear(callback) {
 }
 
 function update(id, app, callback) {
+    // ts is useful as a versioning mechanism (for example, icon changed). update the timestamp explicity in code instead of db.
+    // this way health and healthTime can be updated without changing ts
+    app.ts = new Date();
     updateWithConstraints(id, app, '', callback);
 }
 
@@ -457,7 +460,7 @@ function updateWithConstraints(id, app, constraints, callback) {
 function setHealth(appId, health, healthTime, callback) {
     assert.strictEqual(typeof appId, 'string');
     assert.strictEqual(typeof health, 'string');
-    assert(util.isDate(healthTime));
+    assert(util.types.isDate(healthTime));
     assert.strictEqual(typeof callback, 'function');
 
     var values = { health, healthTime };