fix(alert): make deprecated controller work with 1.3.x

Closes #4576

Author: Foxandxss

src/alert/alert.js

@@ -37,10 +37,10 @@ angular.module('ui.bootstrap.alert')
       $log.warn('AlertController is now deprecated. Use UibAlertController instead.');
     }
 
-    return $controller('UibAlertController', {
+    angular.extend(this, $controller('UibAlertController', {
       $scope: $scope,
       $attrs: $attrs
-    });
+    }));
   }])
 
   .directive('alert', ['$log', '$alertSuppressWarning', function($log, $alertSuppressWarning) {