HMAC-BLAKE2 algorithms compute incorrect results

When used in conjunction with the Hash-based Message Authentication Code (HMAC),
the BLAKE2b and BLAKE2s implementations in blake2 crate versions prior to
v0.8.1 used an incorrect block size (32-bytes instead of 64-bytes for BLAKE2s,
and 64-bytes instead of 128-bytes for BLAKE2b), causing them to miscompute the
MacResult.

The v0.8.1 release of the blake2 crate uses the correct block sizes.

Note that this advisory only impacts usage of BLAKE2 with HMAC, and does not
impact Digest functionality.