chore: update TODO

Author: panva

lib/helpers/client.js

@@ -10,6 +10,7 @@ const { keystores } = require('./weak_cache');
 const merge = require('./merge');
 
 // TODO: in v6.x additionally encode the `- _ . ! ~ * ' ( )` characters
+// https://github.com/panva/node-openid-client/commit/5a2ea80ef5e59ec0c03dbd97d82f551e24a9d348
 const formUrlEncode = (value) => encodeURIComponent(value).replace(/%20/g, '+');
 
 async function clientAssertion(endpoint, payload) {