message: Use a slice instead of a vector in prf_expand()
diff: @@ -12,7 +12,7 @@ pub const PRF_EXPAND_PERSONALIZATION: &'static [u8; 16] = b"Zcash_ExpandSeed";
  /// PRF^expand(sk, t) := BLAKE2b-512("Zcash_ExpandSeed", sk || t)
  pub fn prf_expand(sk: &[u8], t: &[u8]) -> Blake2bResult {
  - prf_expand_vec(sk, &vec![t])
  + prf_expand_vec(sk, &[t])
  }
  pub fn prf_expand_vec(sk: &[u8], ts: &[&[u8]]) -> Blake2bResult {
  