fix(swipe): safe apply the callback

Fixes the swipe directive occasionally throwing "$digest in progress" errors.

Fixes #8318.

src/components/swipe/swipe.js

@@ -81,12 +81,12 @@ function getDirective(name) {
   return DirectiveFactory;
 
   /* @ngInject */
-  function DirectiveFactory($parse) {
+  function DirectiveFactory($parse, $mdUtil) {
       return { restrict: 'A', link: postLink };
       function postLink(scope, element, attr) {
         var fn = $parse(attr[directiveName]);
         element.on(eventName, function(ev) {
-          scope.$apply(function() { fn(scope, { $event: ev }); });
+          $mdUtil.nextTick(function() { fn(scope, { $event: ev }); });
         });
       }
     }