Updated readme.txt (changed an URL)

git-svn-id: https://plugins.svn.wordpress.org/purple-heart-rating-free/trunk@851794 b8457f37-d9ea-0310-8a92-e5e31aec5664
Updated readme.txt (changed an URL)

git-svn-id: https://plugins.svn.wordpress.org/purple-heart-rating-free/trunk@851796 b8457f37-d9ea-0310-8a92-e5e31aec5664