Fixed an issue with post_image field

git-svn-id: https://plugins.svn.wordpress.org/gravity-forms-sticky-list/trunk@1055269 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated readme.txt

git-svn-id: https://plugins.svn.wordpress.org/gravity-forms-sticky-list/trunk@1055270 b8457f37-d9ea-0310-8a92-e5e31aec5664