Node Replace

sample_replace.js

var mongo 			= require('mongoskin');

var db = mongo.db("mongodb://localhost/learnmongo");
db.bind('sample');

var test1 = {
	first: 'Jane',
	last: 'Doe',
	sex: 'female'
}

var test2 = {
	first: 'John',
	last: 'Doe',
	sex: 'male'
}

db.sample.insert(test1, function(err, result){
	console.log('=== Initial Result ===');
 	console.log(err, result);
 	var objId = mongo.helper.toObjectID(result.ops[0]._id)
 	db.sample.replaceOne(
		{_id:  objId},
		test2,
		{upsert: false},
		function(err, rslt){
			console.log('=== Update Result ===');
			console.log(err, rslt.result);
			return;
		}
	);
});

This returns

=== Initial Result ===
null { result: { ok: 1, n: 1 },
  ops:
   [ { first: 'Jane',
       last: 'Doe',
       sex: 'female',
       _id: 565a62b6f573360649e79ebb } ],
  insertedCount: 1,
  insertedIds: [ 565a62b6f573360649e79ebb ] }
=== Update Result ===
null { ok: 1, nModified: 0, n: 0 }

Why doesn't the second record replace the first record? What am I missing