Update package.json

trying make express dependency more strict to avoid error message on startup:

var app = module.exports.app = express.createServer();
                                       ^
TypeError: Object function createApplication() {
  var app = function(req, res, next) {
    app.handle(req, res, next);
  };

  mixin(app, proto);
  mixin(app, EventEmitter.prototype);

  app.request = { __proto__: req, app: app };
  app.response = { __proto__: res, app: app };
  app.init();
  return app;
} has no method 'createServer'
    at Object.<anonymous> (C:\Users\bfrancisoud\AppData\Roaming\npm\node_modules\mongodb-rest\server.js:26:40)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Module.require (module.js:364:17)
    at require (module.js:380:17)
    at Object.<anonymous> (C:\Users\bfrancisoud\AppData\Roaming\npm\node_modules\mongodb-rest\bin\mongodb-rest:8:17)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)