Updated readme.txt

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-natural-sort-for-products/trunk@907749 b8457f37-d9ea-0310-8a92-e5e31aec5664
typo in readme.txt

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-natural-sort-for-products/trunk@907751 b8457f37-d9ea-0310-8a92-e5e31aec5664