fix(demo): fix list demo secondary action.

event is not defined as argument of `doSecondaryAction()`

Closes #2471.

Author: alirezamirian

src/components/list/demoListControls/script.js

@@ -53,7 +53,7 @@ angular.module('listDemo2', ['ngMaterial'])
     );
   };
 
-  $scope.doSecondaryAction = function() {
+  $scope.doSecondaryAction = function(event) {
     $mdDialog.show(
       $mdDialog.alert()
         .title('Secondary Action')