Make nk the first argument to Nullifier::derive

This more closely matches DeriveNullifier in the spec.

src/note.rs

@@ -73,7 +73,7 @@ impl Note {
 
     /// Derives the nullifier for this note.
     pub fn nullifier(&self, fvk: &FullViewingKey) -> Nullifier {
-        Nullifier::derive(self.rho.0, self.rseed.psi(), self.commitment(), fvk.nk())
+        Nullifier::derive(fvk.nk(), self.rho.0, self.rseed.psi(), self.commitment())
     }
 }
 

src/note/nullifier.rs

@@ -18,10 +18,10 @@ impl Nullifier {
     ///
     /// [commitmentsandnullifiers]: https://zips.z.cash/protocol/nu5.pdf#commitmentsandnullifiers
     pub(super) fn derive(
+        nk: &NullifierDerivingKey,
         rho: pallas::Base,
         psi: pallas::Base,
         cm: NoteCommitment,
-        nk: &NullifierDerivingKey,
     ) -> Self {
         let k = pallas::Point::hash_to_curve("z.cash:Orchard")(b"K");