message: pass callback to yargs warning about mnemonic
diff: @@ -348,8 +348,10 @@ const {
  .help().argv as Options;
  if (!mnemonic) {
  - yargs.showHelp(
  + yargs.showHelp(() =>
  + console.log(
  'No mnemonic is defined, either specify the mnemonic as a positional arg or pass it in using the MNEMONIC_PHRASE env var'
  + )
  );
  process.exit(1);
  }
  