Replace rust-crypto with sha2 in sapling-crypto dev-dependencies

This removes rand < 0.5 from our Cargo.lock.

sapling-crypto/Cargo.toml

@@ -23,4 +23,4 @@ byteorder = "1"
 
 [dev-dependencies]
 hex-literal = "0.1"
-rust-crypto = "0.2"
+sha2 = "0.8"

sapling-crypto/src/circuit/sha256.rs

@@ -370,8 +370,7 @@ mod test {
 
     #[test]
     fn test_against_vectors() {
-        use crypto::sha2::Sha256;
-        use crypto::digest::Digest;
+        use sha2::{Digest, Sha256};
 
         let mut rng = XorShiftRng::from_seed([
             0x59, 0x62, 0xbe, 0x3d, 0x76, 0x3d, 0x31, 0x8d, 0x17, 0xdb, 0x37, 0x32, 0x54, 0x06, 0xbc,
@@ -383,8 +382,7 @@ mod test {
             let mut h = Sha256::new();
             let data: Vec<u8> = (0..input_len).map(|_| rng.gen()).collect();
             h.input(&data);
-            let mut hash_result = [0u8; 32];
-            h.result(&mut hash_result[..]);
+            let hash_result = h.result();
 
             let mut cs = TestConstraintSystem::<Bls12>::new();
             let mut input_bits = vec![];

sapling-crypto/src/lib.rs

@@ -12,7 +12,7 @@ extern crate byteorder;
 extern crate hex_literal;
 
 #[cfg(test)]
-extern crate crypto;
+extern crate sha2;
 
 pub mod jubjub;
 pub mod group_hash;