Migrate remaining crates to rand_core 0.4

zcash_proofs/src/lib.rs

@@ -3,7 +3,7 @@ extern crate blake2b_simd;
 extern crate byteorder;
 extern crate ff;
 extern crate pairing;
-extern crate rand;
+extern crate rand_os;
 extern crate sapling_crypto;
 extern crate zcash_primitives;
 

zcash_proofs/src/sapling/prover.rs

@@ -3,7 +3,7 @@ use bellman::groth16::{
 };
 use ff::Field;
 use pairing::bls12_381::{Bls12, Fr};
-use rand::OsRng;
+use rand_os::OsRng;
 use sapling_crypto::{
     circuit::{
         multipack,