message: cargo fix --edition-idioms for librustzcash
diff: -extern crate bellman;
  -extern crate blake2b_simd;
  -extern crate blake2s_simd;
  -extern crate byteorder;
  -extern crate ff;
  -extern crate libc;
  -extern crate pairing;
  -extern crate rand_core;
  -extern crate rand_os;
  -extern crate zcash_primitives;
  -extern crate zcash_proofs;
  -
  -extern crate lazy_static;
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  +use lazy_static;
  use ff::{PrimeField, PrimeFieldRepr};
  use pairing::bls12_381::{Bls12, Fr, FrRepr};
  