Merge pull request reactjs#150 from luisherranz/patch-1

Fix `listenBeforeLeavingRoute` error

Author: timdorr

lessons/13-server-rendering/README.md

@@ -37,7 +37,7 @@ module.exports = {
 
   // keep node_module paths out of the bundle
   externals: fs.readdirSync(path.resolve(__dirname, 'node_modules')).concat([
-    'react-dom/server'
+    'react-dom/server', 'react/addons',
   ]).reduce(function (ext, mod) {
     ext[mod] = 'commonjs ' + mod
     return ext