Fixed a bug related to header

git-svn-id: https://plugins.svn.wordpress.org/link-preview/trunk@1011930 b8457f37-d9ea-0310-8a92-e5e31aec5664
Added preview

git-svn-id: https://plugins.svn.wordpress.org/link-preview/trunk@1011931 b8457f37-d9ea-0310-8a92-e5e31aec5664
Added preview

git-svn-id: https://plugins.svn.wordpress.org/link-preview/trunk@1011934 b8457f37-d9ea-0310-8a92-e5e31aec5664