bug with variable widget_type

Variable “widget_type” does not exist in SonataAdminBundle:Form:filter_admin_fields.html.twig
* http://stackoverflow.com/questions/23004015/variable-widget-type-does-not-exist-in-sonataadminbundleformfilter-admin-fie

* http://stackoverflow.com/questions/22985378/sonata-admin-filters-should-looks-like-set-of-checkboxes-but-got-error
Merge pull request #2067 from BupycHuk/patch-2

bug with variable widget_type