remove findDOMNode from searchbar

[ryouaki]

在官网的描述中有如下的描述，官网也不是建议使用这个api，而在配合redux使用的时候，findDOMNode会有返回null的情况(在ref回调中，这里在onclick应该是没问题的)。但是本身searchInput已经存在于this.refs中了。因此没必要再使用findDOMNode了。

ReactDOM.findDOMNode(component)
If this component has been mounted into the DOM, this returns the corresponding native browser DOM element. This method is useful for reading values out of the DOM, such as form field values and performing DOM measurements. In most cases, you can attach a ref to the DOM node and avoid using findDOMNode at all. When render returns null or false, findDOMNode returns null.

[coveralls]

Coverage decreased (-0.2%) to 88.553% when pulling e43fcb2 on react-redux-mvvm:master into 21c7ade on weui:master.