Change comment to "register extensions via pull-req".

bip-0070/paymentrequest.proto

@@ -2,8 +2,8 @@
 // Simple Bitcoin Payment Protocol messages
 //
 // Use fields 100+ for extensions;
-// to avoid conflicts, register extensions at:
-// https://en.bitcoin.it/wiki/Payment_Request
+// to avoid conflicts, register extensions via pull-req at:
+// https://github.com/bitcoin/bips
 //
 
 package payments;