add dropdown style screenshot

git-svn-id: https://plugins.svn.wordpress.org/yith-woocommerce-ajax-navigation/trunk@836011 b8457f37-d9ea-0310-8a92-e5e31aec5664
Error on README.txt

git-svn-id: https://plugins.svn.wordpress.org/yith-woocommerce-ajax-navigation/trunk@836012 b8457f37-d9ea-0310-8a92-e5e31aec5664