Refresh gift_card and hello_world examples.

examples/hello_world/aiken.lock

@@ -13,4 +13,4 @@ requirements = []
 source = "github"
 
 [etags]
-"aiken-lang/stdlib@v2" = [{ secs_since_epoch = 1725021976, nanos_since_epoch = 403974000 }, "cdbbce58b61deb385e7ea787a2e0fc2dc8fe94db9999e0e6275bc9c70e5796be"]
+"aiken-lang/stdlib@v2" = [{ secs_since_epoch = 1725207187, nanos_since_epoch = 801664000 }, "d79382d2b6ecb3aee9b0755c31d8a5bbafe88a7b3706d7fb8a52fd4d05818501"]

examples/hello_world/validators/hello_world.ak

@@ -1,5 +1,5 @@
 use aiken/collection/list
-use cardano/credential.{VerificationKeyHash}
+use aiken/crypto.{VerificationKeyHash}
 use cardano/transaction.{OutputReference, Transaction}
 
 pub type Datum {
@@ -16,7 +16,7 @@ validator hello_world {
     redeemer: Redeemer,
     _: OutputReference,
     transaction: Transaction,
-  ) -> Bool {
+  ) {
     let must_say_hello = redeemer.msg == "Hello, World!"
 
     expect Some(Datum { owner }) = datum