update to latest blake2-rfc

zcash_wallet/README.md

@@ -4,17 +4,4 @@ This library contains Rust structs and traits for creating shielded Zcash wallet
 
 ## License
 
-Licensed under either of
-
- * Apache License, Version 2.0, ([LICENSE-APACHE](LICENSE-APACHE) or http://www.apache.org/licenses/LICENSE-2.0)
- * MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
-
-at your option.
-
-### Contribution
-
-Unless you explicitly state otherwise, any contribution intentionally
-submitted for inclusion in the work by you, as defined in the Apache-2.0
-license, shall be dual licensed as above, without any additional terms or
-conditions.
-
+GPLv3