removed createClass usage from track component

Author: akiran

src/track.js

@@ -3,7 +3,6 @@
 import React from 'react';
 import assign from 'object-assign';
 import classnames from 'classnames';
-import createReactClass from 'create-react-class';
 
 var getSlideClasses = (spec) => {
   var slickActive, slickCenter, slickCloned;
@@ -141,13 +140,13 @@ var renderSlides = function (spec) {
 
 };
 
-export var Track = createReactClass({
-  render: function () {
+export class Track extends React.Component {
+  render() {
     var slides = renderSlides.call(this, this.props);
     return (
       <div className='slick-track' style={this.props.trackStyle}>
         { slides }
       </div>
     );
   }
-});
+}