Add Meteor.users = new Meteor.Collection('users')

Although this is very easy to do with project specific stubs, I think it's good to have `Meteor.users = new Meteor.Collection('users')` as part of `meteor-stubs.js` since Meteor.users is a collection created by Meteor automatically, so it's less of a "surprise factor" for noobs (such as admittedly - myself)
Merge pull request #38 from rantav/patch-1

Add Meteor.users = new Meteor.Collection('users')