Update plugin for compatibility with WordPress 3.9

git-svn-id: https://plugins.svn.wordpress.org/tinymce-spellcheck/trunk@897567 b8457f37-d9ea-0310-8a92-e5e31aec5664
Update stable tag to 1.2

git-svn-id: https://plugins.svn.wordpress.org/tinymce-spellcheck/trunk@897569 b8457f37-d9ea-0310-8a92-e5e31aec5664