Revert export change to ES6 - breaks Node

Author: STRML

README.md

@@ -19,6 +19,7 @@ See the [demo](/test/TestLayout.jsx) for more on this.
 ### Usage
 
 ```javascript
+var Resizable = require('react-resizable').Resizable; // or,
 var ResizableBox = require('react-resizable').ResizableBox;
 
 ...

index.js

@@ -1,7 +1,7 @@
-export default function() {
-  throw new Error("Don't instantiate Resizable directly! Use require('react-resizable').Resizable or " +
-                  "import {Resizable} from 'react-resizable'.");
+'use strict';
+module.exports = function() {
+  throw new Error("Don't instantiate Resizable directly! Use require('react-resizable').Resizable");
 };
 
-export Resizable from './build/Resizable';
-export ResizableBox from './build/ResizableBox';
+module.exports.Resizable = require('./build/Resizable');
+module.exports.ResizableBox = require('./build/ResizableBox');