Fix broken link in transfer-hook interface Readme.md (#6154)

Fix typo

Author: GabrielePicco

token/transfer-hook/interface/README.md

@@ -142,7 +142,7 @@ program:
 
 The `spl-transfer-hook-interface` library provides offchain and onchain helpers
 for resolving the additional accounts required. See
-[invoke.rs](https://github.com/solana-labs/solana-program-library/tree/master/token/transfer-hook/interface/src/invoke.rs)
+[onchain.rs](https://github.com/solana-labs/solana-program-library/tree/master/token/transfer-hook/interface/src/onchain.rs)
 for usage on-chain, and
 [offchain.rs](https://github.com/solana-labs/solana-program-library/tree/master/token/transfer-hook/interface/src/offchain.rs)
 for fetching the additional required account metas with any async off-chain client