DEP 0002: add missing rust tags to codeblock

doc/src/dep/0002.md

@@ -70,7 +70,7 @@ streaming contract making calls on a ZK NFT.
 
 The current `ContractCall` struct looks like:
 
-```
+```rust
 pub struct ContractCall {
     /// ID of the contract invoked
     pub contract_id: ContractId,
@@ -81,7 +81,7 @@ pub struct ContractCall {
 
 We propose to change the `data` field to this:
 
-```
+```rust
 pub struct ContractCall {
     /// ID of the contract invoked
     pub contract_id: ContractId,