Node.js and Mongodb - TypeError: undefined is not a function

my friend and I are trying to create a basic webapp with Node.js and MongoDB, and we've ran into a problem while trying to connect to the database. The error that we're receiving is as follows:

C:\Users\James Kienle\Dropbox\Apps\Azure\Hanky-Ranky\server.js:24 mongoClient.open(function(err, mongoClient) { //C ^ TypeError: undefined is not a function at Object. (C:\Users\James Kienle\Dropbox\Apps\Azure\Hanky-Ranky\server.js:24:13) at Module._compile (module.js:460:26) at Object.Module._extensions..js (module.js:478:10) at Module.load (module.js:355:32) at Function.Module._load (module.js:310:12) at Function.Module.runMain (module.js:501:10) at startup (node.js:129:16) at node.js:814:3

Here's server.js, our main file

// Bring in required references
var http = require('http'),
    express = require('express'),
    path = require('path'),
    MongoClient = require('mongodb').MongoClient,
    Server = require('mongodb').Server,
    CollectionDriver = require('./collectionDriver').CollectionDriver;

// Set the default port for the app
var port = process.env.PORT || 1337;

// Create the new express app and set all required variables such as port and static html path
var app = express();
app.set('port', port); 
app.set('views', path.join(__dirname, 'views'));
app.set('view engine', 'jade');

// Connect to MongoDB
var mongoHost = 'ds040898.mongolab.com'; //A
var mongoPort = 40898; 
var collectionDriver;

var mongoClient = new MongoClient(new Server(mongoHost, mongoPort)); //B
mongoClient.open(function(err, mongoClient) { //C
  if (!mongoClient) {
      console.error("Error! Exiting... Must start MongoDB first");
      process.exit(1); //D
  }
  var db = mongoClient.db("MongoLab-0");  //E
  db.authenticate('testuser', 'testpassword', function(err, result) {
    collectionDriver = new CollectionDriver(db); //F
  });
});

// Set up the expressjs public path
app.use(express.static(path.join(__dirname, 'public')));

// BRING IN THE DATA
app.get('/:collection', function(req, res) { //A
   var params = req.params; //B
   collectionDriver.findAll(req.params.collection, function(error, objs) { //C
          if (error) { res.send(400, error); } //D
          else { 
              if (req.accepts('html')) { //E
                  res.render('data',{objects: objs, collection: req.params.collection}); //F
              } else {
              res.set('Content-Type','application/json'); //G
                  res.send(200, objs); //H
              }
         }
    });
});

app.get('/:collection/:entity', function(req, res) { //I
   var params = req.params;
   var entity = params.entity;
   var collection = params.collection;
   if (entity) {
       collectionDriver.get(collection, entity, function(error, objs) { //J
          if (error) { res.send(400, error); }
          else { res.send(200, objs); } //K
       });
   } else {
      res.send(400, {error: 'bad url', url: req.url});
   }
});

// Pull the template for a 404 page
app.use(function (req,res) {
    res.render('404', {url:req.url}); 
});

// Create the node server
http.createServer(app).listen(app.get('port'), function(){
  console.log('Express server listening on port ' + app.get('port'));
});

And here's CollectionDriver.js

// Import the required MongoDB Packages
var ObjectID = require('mongodb').ObjectID;

// Define the CollectionDriver constructor method for later use
CollectionDriver = function(db) {
  this.db = db;
};

// Fetch a collection by name
CollectionDriver.prototype.getCollection = function(collectionName, callback) {
  this.db.collection(collectionName, function(error, the_collection) {
    if( error ) callback(error);
    else callback(null, the_collection);
  });
};

// Return all found objects
CollectionDriver.prototype.findAll = function(collectionName, callback) {
    this.getCollection(collectionName, function(error, the_collection) { //A
      if( error ) callback(error);
      else {
        the_collection.find().toArray(function(error, results) { //B
          if( error ) callback(error);
          else callback(null, results);
        });
      }
    });
};

// Obtain and display a single item vie _id
CollectionDriver.prototype.get = function(collectionName, id, callback) { //A
    this.getCollection(collectionName, function(error, the_collection) {
        if (error) callback(error);
        else {
            var checkForHexRegExp = new RegExp("^[0-9a-fA-F]{24}$"); //B
            if (!checkForHexRegExp.test(id)) callback({error: "invalid id"});
            else the_collection.findOne({'_id':ObjectID(id)}, function(error,doc) { //C
                if (error) callback(error);
                else callback(null, doc);
            });
        }
    });
};

exports.CollectionDriver = CollectionDriver;

And here's our package.json file. All of the dependencies listed in this file have been installed properly to my knowledge

{
  "name": "hanky-ranky",
  "version": "1.0.0",
  "private": true,
  "dependencies": {
    "express": "4.13.3",
    "jade": "1.11.0",
    "mongodb":"2.0.42"
  }
}

If it helps, I'm trying to follow a tutorial from this website: http://www.raywenderlich.com/61078/write-simple-node-jsmongodb-web-service-ios-app

Thanks guys! Really appreciate the help!