Add parent call in user.format to fix dateTime

closes #5066

- fix a problem that user model will fail to save if mysql has option of
STRICT_TRANS_TABLES
- add a parent call in user.format override function, which should fix
dateTime format before user saved.

core/server/models/user.js

@@ -110,7 +110,7 @@ User = ghostBookshelf.Model.extend({
             protocols: ['http', 'https']})) {
             options.website = 'http://' + options.website;
         }
-        return options;
+        return ghostBookshelf.Model.prototype.format.call(this, options);
     },
 
     posts: function () {