Merge pull request microsoft#750 from vers-one/master

Fix for ESLint "Unexpected trailing comma" warning

Author: mhegazy

pages/tutorials/React & Webpack.md

@@ -224,7 +224,7 @@ module.exports = {
     externals: {
         "react": "React",
         "react-dom": "ReactDOM"
-    },
+    }
 };
 ```