title: find and modify obejct in mlab collection by _id with nodejs
body: <p>i am posting an object to update the current one. Searching by id and replacing it. For some reason i don't get errors but the mlab object is not updated. Am i missing something?    </p>
  
  <pre><code>app.post("/api/updateCheck", function (req, res) {
  console.log('updating', req.body);
  conn.collection("checks").findAndModify({
  _id: req.body._id
  },  {$set: req.body}, {}, function(err,doc) {
  if (err) { console.log(err) }
  else { console.log("Updated"); }
  });  
  });
  </code></pre>