Better keccac256 (#41)

* Switch to keccac256 implementation from golang.org/x/crypto instead of go-ethereum

keccak256/keccac256.go

@@ -0,0 +1,14 @@
+package keccak256
+
+import (
+	"golang.org/x/crypto/sha3"
+)
+
+// Hash generates a Keccak256 hash from a byte array
+func Hash(data ...[]byte) []byte {
+	hash := sha3.NewLegacyKeccak256()
+	for _, d := range data {
+		hash.Write(d) //nolint:errcheck,gosec
+	}
+	return hash.Sum(nil)
+}