Compatibility with JetPack plugin Mobile Theme

git-svn-id: https://plugins.svn.wordpress.org/gallery-slice/trunk@929028 b8457f37-d9ea-0310-8a92-e5e31aec5664
Release 1.2.1

git-svn-id: https://plugins.svn.wordpress.org/gallery-slice/trunk@929030 b8457f37-d9ea-0310-8a92-e5e31aec5664