update slider example

examples/simple.js

@@ -1,6 +1,7 @@
 'use strict';
 
 require('rc-slider/assets/index.css');
+require('rc-tooltip/assets/bootstrap.css');
 var Slider = require('rc-slider');
 var React = require('react');
 // React.render(<Slider marks={["一","二","三","四","五"]} index={3}/>, document.getElementById('__react-content'));