update referer version

git-svn-id: https://plugins.svn.wordpress.org/groupdocs-viewer/trunk@802944 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated readme file

git-svn-id: https://plugins.svn.wordpress.org/groupdocs-viewer/trunk@804735 b8457f37-d9ea-0310-8a92-e5e31aec5664