Update to version 1.3.1.

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-plivo/trunk@1007105 b8457f37-d9ea-0310-8a92-e5e31aec5664
Version 1.3.1 release.

git-svn-id: https://plugins.svn.wordpress.org/woocommerce-plivo/trunk@1007106 b8457f37-d9ea-0310-8a92-e5e31aec5664