bip-325: update PR link

Author: bitschmidty

bip-0325.mediawiki

@@ -89,7 +89,7 @@ Other software need not add block signature validation code that they will not u
 
 == Reference implementation ==
 
-Pull request at https://github.com/bitcoin/bitcoin/pull/16411
+Pull request at https://github.com/bitcoin/bitcoin/pull/18267
 
 == Acknowledgements ==