message: Fix rand_os warning in tests
diff: @@ -186,8 +186,7 @@ pub fn scan_block(
  mod tests {
  use ff::{Field, PrimeField, PrimeFieldRepr};
  use pairing::bls12_381::{Bls12, Fr};
  - use rand_core::RngCore;
  - use rand_os::OsRng;
  + use rand_core::{OsRng, RngCore};
  use zcash_primitives::{
  jubjub::{fs::Fs, FixedGenerators, JubjubParams, ToUniform},
  merkle_tree::CommitmentTree,
  