expire cached tracking ids when they are updated

git-svn-id: https://plugins.svn.wordpress.org/productwidgets/trunk@989437 b8457f37-d9ea-0310-8a92-e5e31aec5664
tagged version v1.0.3

git-svn-id: https://plugins.svn.wordpress.org/productwidgets/trunk@989438 b8457f37-d9ea-0310-8a92-e5e31aec5664