title: How to decrement like $dec?
body: <p>In the Meteor leaderboard example there is this line:</p>
  
  <pre><code>  Players.update(Session.get("selected_player"), {$inc: {score: 5}});
  </code></pre>
  
  <p>How can I gracefully decrement the same field? Sadly, there is no $dec.</p>