title: ionicPopup cannot get input value
body: <p>I follow the sample of <a href="http://ionicframework.com/docs/api/service/$ionicPopup/" rel="nofollow noreferrer">$ionicPopup.show here</a> but fail.</p>
  
  <pre><code>angular.module('main').directive('dtDiscount', function($ionicPopup) {
      return {
          require: 'ngModel',
          scope: {
              operators: '=operators',
              toggle: '=toggle',
          },
          templateUrl: 'templates/components/discount.html',
          link: function ($scope, $element, $attrs, ctrl) {
  
              $scope.customeDiscount = 0;
              $scope.setCustomDiscount = function(){
                  $ionicPopup.show({
                      title: 'Input Your Own Discount',
                      subTitle: 'XX %off',
                      template: '&lt;input type="number" ng-model="customeDiscount"/&gt;', // the preset value show 0, which is expected.
                      scope: $scope,
                      buttons: [{ text: 'Cancel' },{
                          text: '&lt;b&gt;Confirm&lt;/b&gt;',
                          type: 'button-positive',
                          onTap: function(e) {
                              console.log($scope.customeDiscount); // 0
                              return $scope.customeDiscount;
                          }
                      }]
                  });
              }
  
              $scope.$watch('customeDiscount', function(value){
                  console.log(value);
              });
          }
      }
  })
  </code></pre>
  
  <p>Whatever I input any value for customeDiscount, it always gives me <code>0</code> output, such that the value <code>$scope.customeDiscount</code> cannot be changed.</p>
  
  <p>Can someone help me to find out what is the problem?</p>