[LayaAir 2.0]Slider控件的标签不居中

		protected function showValueText():void {

			if (showLabel) {

				var label:Label = Slider.label;

				addChild(label);

				label.textField.changeText(_value + "");

				if (isVertical) {

					label.x = _bar._x + 20;

					label.y = (_bar.height - label.height) * 0.5 + _bar._y;

				} else {

					label.y = _bar._y - 20;

					label.x = (_bar.width - label.width) * 0.5 + _bar._x;

				}

			}

		}