LibreSSL doesn't implement blake2.

Index: util/hmac.lua
--- util/hmac.lua.orig
+++ util/hmac.lua
@@ -17,6 +17,4 @@ return {
 	sha256 = hashes.hmac_sha256,
 	sha384 = hashes.hmac_sha384,
 	sha512 = hashes.hmac_sha512,
-	blake2s256 = hashes.hmac_blake2s256,
-	blake2b512 = hashes.hmac_blake2b512,
 };
