fix(alert): properly pass $event as local

- Change to pass object due to how `&` binding works

Fixes #4386
Closes #4387

Author: wesleycho

template/alert/alert.html

@@ -1,5 +1,5 @@
 <div class="alert" ng-class="['alert-' + (type || 'warning'), closeable ? 'alert-dismissible' : null]" role="alert">
-    <button ng-show="closeable" type="button" class="close" ng-click="close($event)">
+    <button ng-show="closeable" type="button" class="close" ng-click="close({$event: $event})">
         <span aria-hidden="true">&times;</span>
         <span class="sr-only">Close</span>
     </button>