code: function (keys) {
      var Parent = this.constructor;
      var opts = lazy.clone(this.options);
      var res = new Parent(opts);
  
      lazy.omit(this, keys, function (val, key) {
        res[key] = lazy.clone(val);
      });
      return res;
    }
docs: Return a clone of the instance.
  
  ```js
  var foo = app.clone();
  ```
  @param  {Array} keys Optionally pass an array of keys to omit.
  @return {Object}
  @api public