fixed usage of deprecated function nggShowGallery() with NG 2.x; WP 3.6 compatibility checked

git-svn-id: https://plugins.svn.wordpress.org/wunderslider-gallery/trunk@751237 b8457f37-d9ea-0310-8a92-e5e31aec5664
version inc 1.3.6

git-svn-id: https://plugins.svn.wordpress.org/wunderslider-gallery/trunk@751238 b8457f37-d9ea-0310-8a92-e5e31aec5664