message: browser test optional argument
diff: @@ -25,7 +25,7 @@ fn key_derive() {
  let path = "m/44'/461'/0/0/1".to_string();
  let answer =
  - filecoin_signer_wasm::key_derive(mnemonic, path, "".to_string(), &"en".to_string())
  + filecoin_signer_wasm::key_derive(mnemonic, path, "".to_string(), Option("en".to_string()))
  .expect("unexpected error");
  assert_eq!(
  