Added upgrade.php to track version changes.

git-svn-id: https://plugins.svn.wordpress.org/datafeedr-woocommerce-importer/trunk@902630 b8457f37-d9ea-0310-8a92-e5e31aec5664
Fixed path to upgrade.php error.

git-svn-id: https://plugins.svn.wordpress.org/datafeedr-woocommerce-importer/trunk@902633 b8457f37-d9ea-0310-8a92-e5e31aec5664