fix(specs/withdrawal): Sherlock #166

Based on https://github.com/sherlock-audit/2023-01-optimism-judging/blob/b7921698c1c537714c5f2021aa46ce0a1935ba39/1-specs-findings/1-processed/1-true/portal-interface/166.md#L1

specs/withdrawals.md

@@ -139,7 +139,8 @@ withdrawals:
 ```js
 interface OptimismPortal {
 
-    event WithdrawalFinalized(bytes32 indexed);
+    event WithdrawalFinalized(bytes32 indexed withdrawalHash, bool success);
+
 
     function l2Sender() returns(address) external;