Throw validation error's instead of calling Deno.exit() to handle validation error's manually.

A validation error is thrown when the command is wrongly used by the user. For example: If the user passes some invalid options or arguments to the command.

This has no effect for parent commands. Only for the command on which this method was called and all child commands.

Example:

try {
  cmd.parse();
} catch(error) {
  if (error instanceof ValidationError) {
    cmd.showHelp();
    Deno.exit(1);
  }
  throw error;
}