title: Hidden input field in Angularjs not update
body: <p>I use angularjs v1.0.7. I have a hidden form field, which it's value is related with other input value. In  <a href="http://jsfiddle.net/4ANaK/" rel="nofollow">http://jsfiddle.net/4ANaK/</a> example, hidden filed not update as I type in text input filed filed. </p>
  
  <pre><code>&lt;div ng-controller="MyCtrl"&gt;
      &lt;form ng-submit="action()"&gt;
        name:&lt;input ng-model="name" type="text"  value="you name"&gt;
        &lt;input ng-model="nice_name" type="hidden" value="Mr {{name}}" &gt;
        &lt;input type="submit"&gt;
      &lt;/form&gt;
  &lt;/div&gt;
  
  var app=angular.module('myApp', []);
  
  function MyCtrl($scope) {
      $scope.name = "David";
  
      $scope.action = function(){
          alert($scope.nice_name);                
      }
  }
  </code></pre>
  
  <p>How to fixed the problem?</p>