Fix to get this example to run without hiccups

The dependency "express" : "latest" installs Express 4.x. This version of Express has deprecated the app.configure method and hence breaks the experience of trying out the ZeroClipboard example locally. This pull request is a temporary fix until you update the node_server.js file according to migration guidelines here https://github.com/visionmedia/express/wiki/Migrating-from-3.x-to-4.x