update to 1.3.1

git-svn-id: https://plugins.svn.wordpress.org/alipay-for-woocommerce/trunk@998367 b8457f37-d9ea-0310-8a92-e5e31aec5664
update readme.txt

git-svn-id: https://plugins.svn.wordpress.org/alipay-for-woocommerce/trunk@998369 b8457f37-d9ea-0310-8a92-e5e31aec5664