Update nav.adoc

Author: LandauRaz

components/Starknet/modules/architecture-and-concepts/nav.adoc

@@ -3,7 +3,7 @@
     ** xref:transactions.adoc[Transactions]
     ** xref:network-architecture/block-structure.adoc[]
     ** xref:cryptography.adoc[Cryptography]
-    ** xref:network-architecture/fee-mechanism.adoc[Fee mechanism]
+    ** xref:network-architecture/fee-mechanism.adoc[Fees]
     ** xref:network-architecture/messaging-mechanism.adoc[L1-L2 messaging]
     ** xref:network-architecture/data-availability.adoc[Data availability]
     ** xref:smart-contracts/serialization-of-cairo-types.adoc[Serialization]