update to 2.9

git-svn-id: https://plugins.svn.wordpress.org/jetpack-gravatar-hovercards/trunk@868385 b8457f37-d9ea-0310-8a92-e5e31aec5664
update stable tag in readme

git-svn-id: https://plugins.svn.wordpress.org/jetpack-gravatar-hovercards/trunk@868394 b8457f37-d9ea-0310-8a92-e5e31aec5664
minor improvements

git-svn-id: https://plugins.svn.wordpress.org/jetpack-gravatar-hovercards/trunk@869520 b8457f37-d9ea-0310-8a92-e5e31aec5664