update ScrollDepth library. Update tested version for WordPress 4.1

git-svn-id: https://plugins.svn.wordpress.org/wp-scroll-depth/trunk@1051813 b8457f37-d9ea-0310-8a92-e5e31aec5664
update ScrollDepth library.

git-svn-id: https://plugins.svn.wordpress.org/wp-scroll-depth/trunk@1051815 b8457f37-d9ea-0310-8a92-e5e31aec5664