title: Mongoose update not updating
body: <p>I'm trying to update a document which has a specific ID with the current date/time but the below code is not resulting in the DB getting updated and no errors. Any help would be great, thanks.</p>
  
  <p>Schema:</p>
  
  <pre><code>var MerchantShema = new Schema({
      merchant_id: Number,
      merchant_aw_id: Number,
      merchant_name: String,
      merchant_url: String,
      merchant_image: String,
      product_feed: String,
      product_feed_updated: Date,
      created_at: {type: Date, default: Date.now},
      updated_at: {type: Date, default: Date.now}
  });
  </code></pre>
  
  <p>Update Query:</p>
  
  <pre><code>updateMerchantLastProductUpdate: function (mID) {
    now = new Date();      
  
    var query = { "merchant_aw_id" : mID };
    Merchants.update(query, { "product_feed_updated": now }, function (err) {
      if (err) return console.error(err);        
    })
  }
  </code></pre>
  
  <p>Route</p>
  
  <pre><code>  app.get('/queries', function (req, res) {
      queries.updateMerchantLastProductUpdate("2926");
    });
  </code></pre>
  
  <p>Example document</p>
  
  <pre><code>{
      "_id": {
          "$oid": "55997638e4b01f0391cb99aa"
      },
      "merchant_id": "0003",
      "merchant_aw_id": "2926",
      "merchant_name": "Multipower",
      "merchant_url": "www.multipower.com/uk/",
      "merchant_image": "",
      "product_feed": "aw",
      "product_feed_updated": "",
      "created_at": "",
      "updated_at": ""
  }
  </code></pre>