fix: add missing link for DHL shipment tracking (#2751)

lib/routes/dhl/shipment-tracking.js

@@ -49,6 +49,7 @@ module.exports = async (ctx) => {
             return {
                 title: checkpoint.description,
                 pubDate: date.toUTCString(),
+                link: `${link}&checkpoint=${encodeURIComponent(checkpoint.counter)}`,
             };
         }),
     };