Use permalink for discussion link

Reported-by: Tzu-ping Chung @uranusjr
Signed-off-by: Philippe Ombredanne <pombredanne@nexb.com>

Author: pombredanne

pep-9999.rst

@@ -5,7 +5,7 @@ Last-Modified: $Date$
 Author: Philippe Ombredanne <pombredanne at nexb.com>
 Sponsor: Paul Moore <p.f.moore at gmail.com>
 BDFL-Delegate: Paul Moore <p.f.moore at gmail.com>
-Discussions-To: https://discuss.python.org/t/improving-license-clarity-with-better-package-metadata
+Discussions-To: https://discuss.python.org/t/2154
 Status: Draft
 Type: Standards Track
 Content-Type: text/x-rst