title: Collection.update() with callback returns undefined
body: <p>In Meteor, I use the return value from Collection.update() (<code>1</code>) on the client to display a message to the user. The method runs on both the client and on the server. </p>
  
  <p>Consider the following method, which works as expected (returns <code>1</code>):</p>
  
  <pre><code>Meteor.methods({
      updateDocument(documentId) {
          return Collection.update(
              documentId, 
              {$set: {updatedBy: this.userId}}
          );
      }
  });
  </code></pre>
  
  <p>Next, consider the following method, which returns <code>undefined</code>:</p>
  
  <pre><code>Meteor.methods({
     updateDocument(documentId) {
          return Collection.update(
              documentId,
              {$set: {updatedBy: this.userId}},
              (error, result) =&gt; {
                  return 1;
              }
          );
      }
  });
  </code></pre>
  
  <p>What am I missing here? Why doesn't <code>updateDocument()</code> return <code>1</code>?</p>