Nowdoc => heredoc in order to support PHP older than 5.3.0

git-svn-id: https://plugins.svn.wordpress.org/document-gallery/trunk@1026457 b8457f37-d9ea-0310-8a92-e5e31aec5664
Minor. Just doing some cleanup.

git-svn-id: https://plugins.svn.wordpress.org/document-gallery/trunk@1026462 b8457f37-d9ea-0310-8a92-e5e31aec5664