title: $watch on checkbox not working
body: <p>I am using <a href="https://github.com/sebastianha/angular-bootstrap-checkbox" rel="nofollow">angular-bootstrap-checkbox</a> like below:</p>
  
  <p><strong>HTML</strong></p>
  
  <pre><code>&lt;checkbox class="checkbox" ng-model="manualPosition"&gt;&lt;/checkbox&gt;
  </code></pre>
  
  <p>I want to watch the changes for the checkbox values. </p>
  
  <p><strong>JS</strong></p>
  
  <pre><code>$scope.$watch('manualPosition', function(manualPosition) {
      console.log('here');
  });
  </code></pre>
  
  <p>It doesn't work for me. </p>