version 2.1.6

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@1027807 b8457f37-d9ea-0310-8a92-e5e31aec5664
updated upgrade notice

git-svn-id: https://plugins.svn.wordpress.org/mailchimp-for-wp/trunk@1027809 b8457f37-d9ea-0310-8a92-e5e31aec5664