Fix bug where no credit was inserted if used on a plain image tag.

git-svn-id: https://plugins.svn.wordpress.org/media-credit/trunk@1047022 b8457f37-d9ea-0310-8a92-e5e31aec5664
Release new version

git-svn-id: https://plugins.svn.wordpress.org/media-credit/trunk@1047023 b8457f37-d9ea-0310-8a92-e5e31aec5664
fix release date

git-svn-id: https://plugins.svn.wordpress.org/media-credit/trunk@1047027 b8457f37-d9ea-0310-8a92-e5e31aec5664