Fix broken links

Author: nc6

src/SUMMARY.md

@@ -20,10 +20,10 @@
   - [`cardano-node`'s ChainDB](storage/cardano-node-chaindb/README.md)
 - [Mempool](mempool/README.md)
 - [Ledger](ledger/README.md)
-  - [Blocks](concepts/blocks.md)
-  - [Determinism](concepts/determinism.md)
-  - [The State Transition Function](state-transition.md)
-    - [Validity](state-transition/validity.md)
+  - [Blocks](ledger/concepts/blocks.md)
+  - [Determinism](ledger/concepts/determinism.md)
+  - [The State Transition Function](ledger/state-transition.md)
+    - [Validity](ledger/state-transition/validity.md)
   - [Transaction fee](ledger/transaction-fee.md)
   - [Block Validation](ledger/block-validation.md)
 - [Plutus](plutus/README.md)