title: $translate.instant('id); not updating when the language changes
body: <p>I have an angular app where two languages are used. I used $translate.instant('id'); in my controller to bind some variables. But when I change the translation language using $translate.use('jp'); The controller variables wont change. </p>
  
  <p>I used 'translate' filter in my HTML. That one will change but controller variables wont change. Is there any way to implement it?</p>
  
  <p>Initialized using the below code.</p>
  
  <pre><code>$translateProvider.useStaticFilesLoader({
    prefix: '/translations/',
    suffix: '.json'
  });
  $translateProvider.preferredLanguage('en');
  $translateProvider.fallbackLanguage('en');
  $translateProvider
    .useSanitizeValueStrategy('escape');
  </code></pre>
  
  <p>In a controller I used the below code.
      vm.userName = $translate.instant('USER_NAME');</p>
  
  <p>When the language change using the below code</p>
  
  <pre><code>$translate.use('jp');
  </code></pre>
  
  <p>The username doesn't change.</p>