Replace var with const in README.md

Author: hiroppy

README.md

@@ -122,9 +122,9 @@ You can use this to remove scrolling on the the body while the modal is open.
 Inside an app:
 
 ```js
-var React = require('react');
-var ReactDOM = require('react-dom');
-var Modal = require('react-modal');
+const React = require('react');
+const ReactDOM = require('react-dom');
+const Modal = require('react-modal');
 
 
 /*
@@ -139,7 +139,7 @@ Modal.setAppElement(appElement);
 Modal.setAppElement('#your-app-element');
 
 */
-var appElement = document.getElementById('your-app-element');
+const appElement = document.getElementById('your-app-element');
 
 
 
@@ -155,7 +155,7 @@ const customStyles = {
 };
 
 
-var App = React.createClass({
+const App = React.createClass({
 
   getInitialState: function() {
     return { modalIsOpen: false };
@@ -202,7 +202,7 @@ var App = React.createClass({
   }
 });
 
-ReactDOM.render(<App/>, appElement);
+ReactDOM.render(<App />, appElement);
 ```
 # Testing