title: nedb method update and delete creates a new entry instead updating existing one
body: <p>I'm using <a href="https://github.com/louischatriot/nedb" rel="nofollow">nedb </a> and I'm trying to update an existing record by matching it's <code>ID</code>, and changing a <code>title</code> property.
  What happens is that a new record gets created, and the old one is still there.
  I've tried several combinations, and tried googling for it, but the search results are scarce.</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var Datastore = require('nedb');
  var db = {
      files: new Datastore({ filename: './db/files.db', autoload: true })
  };
  
  db.files.update(
    {_id: id}, 
    {$set: {title: title}}, 
    {}, 
    callback
  );</code></pre>
  </div>
  </div>
  </p>
  
  <p>What's even crazier when performing a delete, a new record gets added again, but this time the record has a weird property:
  <code>{"$$deleted":true,"_id":"WFZaMYRx51UzxBs7"}</code></p>
  
  <p>This is the code that I'm using:</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>db.files.remove({_id: id}, callback);</code></pre>
  </div>
  </div>
  </p>