message: Fix code snippet typo.
diff: @@ -272,7 +272,7 @@ func main() {
  log.Fatal(err)
  }
  - ct, err := h.Encrypt([]byte("secret message"), []byte("context info"))
  + ct, err := he.Encrypt([]byte("secret message"), []byte("context info"))
  if err != nil {
  log.Fatal(err)
  }
  