update referer version

git-svn-id: https://plugins.svn.wordpress.org/groupdocs-signature/trunk@802950 b8457f37-d9ea-0310-8a92-e5e31aec5664
update referer version

git-svn-id: https://plugins.svn.wordpress.org/groupdocs-signature/trunk@803043 b8457f37-d9ea-0310-8a92-e5e31aec5664
updated readme file

git-svn-id: https://plugins.svn.wordpress.org/groupdocs-signature/trunk@804736 b8457f37-d9ea-0310-8a92-e5e31aec5664