removed dangling comma that messes up loading in IE8

packages/react/react.js

@@ -39,7 +39,7 @@ if (process.env.NODE_ENV !== 'production') {
       'react-dom/server',
       React,
       React.renderToStaticMarkup
-    ),
+    )
   };
   // Export a wrapped object. We'll use assign and take advantage of the fact
   // that this will override the original methods in React.