title: Undefined watchHeading in compass plugin for ionic/phonegap
body: <p>Well, I'm working on a small project made in ionic. I'm using ngCordova to add some cool plugins, like device orientation for compass. But I can't force it to work. I already installed ngCordova and added plugins (geolocation plugin works). I'm out of ideas why this doesn't work.</p>
  
  <p>Code looks like this:</p>
  
  <pre><code>.controller('GeoLocationCtrl', function($scope, $cordovaGeolocation, $cordovaDeviceOrientation, $ionicPlatform, $document) {
  $scope.lat = 0;
  $scope.long = 0;
  $scope.position = {};
  
  
  $ionicPlatform.ready(function() {
  var options = {frequency: 1000}; // Update every 1 second
  var watch2 = $cordovaDeviceOrientation.watchHeading(options); ///LINE 53!
  
  watch2.promise.then(function (result) { /* unused */
      },
      function (err) {
          // An error occurred
      }, function (position) {
          // Heading comes back in
          // position.magneticHeading
          $scope.position = position.magneticHeading;
      });
  
      $cordovaDeviceOrientation.clearWatch(watch2.watchId)
          .then(function (result) {
              // Success!
          }, function (err) {
              // An error occurred
          });
  
    });
  })
  </code></pre>
  
  <p>But all I get is this:</p>
  
  <pre><code>ripple.js:37
  TypeError: Cannot read property 'watchHeading' of undefined
      at Object.watchHeading (http://localhost:8080/lib/ngCordova/dist/ng-        cordova.min.js:1:14565)
      at http://localhost:8080/js/controllers.js:53:44
      at http://localhost:8080/lib/ionic/js/ionic.bundle.js:37388:19
      at Object.ionic.Platform.ready     (http://localhost:8080/lib/ionic/js/ionic.bundle.js:1915:9)
      at Object.self.ready (http://localhost:8080/lib/ionic/js/ionic.bundle.js:37386:26)
      at new &lt;anonymous&gt; (http://localhost:8080/js/controllers.js:15:20)
      at invoke (http://localhost:8080/lib/ionic/js/ionic.bundle.js:11591:17)
      at Object.instantiate (http://localhost:8080/lib/ionic/js/ionic.bundle.js:11602:23)
      at http://localhost:8080/lib/ionic/js/ionic.bundle.js:14906:28
      at updateView (http://localhost:8080/lib/ionic/js/ionic.bundle.js:42986:30) ionic.bundle.js:17696
  </code></pre>
  
  <p>Thanks for any help!</p>