Modifly bls library to reflect recent changes

eth2/utils/bls/Cargo.toml

@@ -9,6 +9,7 @@ bls-aggregates = { git = "https://github.com/sigp/signature-schemes", branch = "
 cached_tree_hash = { path = "../cached_tree_hash" }
 hashing = { path = "../hashing" }
 hex = "0.3"
+rand = "0.5"
 serde = "1.0"
 serde_derive = "1.0"
 serde_hex = { path = "../serde_hex" }

eth2/utils/bls/src/secret_key.rs

@@ -1,3 +1,5 @@
+extern crate rand;
+
 use super::BLS_SECRET_KEY_BYTE_SIZE;
 use bls_aggregates::SecretKey as RawSecretKey;
 use hex::encode as hex_encode;
@@ -16,7 +18,7 @@ pub struct SecretKey(RawSecretKey);
 
 impl SecretKey {
     pub fn random() -> Self {
-        SecretKey(RawSecretKey::random())
+        SecretKey(RawSecretKey::random(&mut rand::thread_rng()))
     }
 
     /// Returns the underlying point as compressed bytes.