README.md: update for eth/68

Author: fjl

README.md

@@ -17,7 +17,7 @@ We have several specifications for low-level protocols:
 
 The repository also contains specifications of many RLPx-based application-level protocols:
 
-- [Ethereum Wire Protocol] (eth/67)
+- [Ethereum Wire Protocol] (eth/68)
 - [Ethereum Snapshot Protocol] (snap/1)
 - [Light Ethereum Subprotocol] (les/4)
 - [Parity Light Protocol] (pip/1)