ch12, middleware does not call 'next' function.

[mrdulin]

12.3.1 section

app.use(function(req,res,next){
  var cluster = require('cluster');
  if(cluster.isWorker) console.log('Worker %d received request',
             cluster.worker.id);
});

should be

app.use(function(req,res,next){
  var cluster = require('cluster');
  if(cluster.isWorker) console.log('Worker %d received request',
             cluster.worker.id);

  next();
});