fix($resource): Delete $cancelRequest from toJSON()

result.toJSON() still include $cancelRequest to the JSON output.
just simply delete it.

Author: hereblur

src/ngResource/resource.js

@@ -636,6 +636,7 @@ angular.module('ngResource', ['ng']).
           var data = extend({}, this);
           delete data.$promise;
           delete data.$resolved;
+          delete data.$cancelRequest;
           return data;
         };