Fix server-server link in IS spec
@@ -247,4 +247,4 @@ this isn't possible.
.. _`Unpadded Base64`: ../appendices.html#unpadded-base64
.. _`3PID Types`: ../appendices.html#pid-types
.. _`Signing JSON`: ../appendices.html#signing-json
-.. _`/3pid/onbind`: ../server_server.html#put-matrix-federation-v1-3pid-onbind
+.. _`/3pid/onbind`: ../server_server/unstable.html#put-matrix-federation-v1-3pid-onbind
