It is important for you to check what version of the Stripe REST API you're currently consuming (via the dashboard). You can explicitly set the version you wish to use like so:

var stripe = require('stripe')('your api key');
stripe.setApiVersion('2013-08-13'); // latest as of 18th Oct 2013

Note: You do not need to set a version explicitly. If you don't set it the Stripe REST API will use your account's default, which you can view under your dashboard (Account Settings » API Keys). Setting a version explicitly via stripe.setApiVersion(...) does not affect your account's default version; it'll only affect the API you consume through that singular stripe instance.

Find more information here: stripe.com/docs/upgrades.