Update a generator.

    Parameters
    ----------
    args : `argparse.Namespace`
        Command arguments.

def cmd_update(args):
    """Update a generator.

    Parameters
    ----------
    args : `argparse.Namespace`
        Command arguments.
    """
    #args.output = None

    markov = load(MarkovText, args.state, args)
    read(args.input, markov, args.progress)
    if args.output is None:
        if args.type == SQLITE:
            save(markov, None, args)
        elif args.type == JSON:
            name, ext = path.splitext(args.state)
            tmp = name + '.tmp' + ext
            save(markov, tmp, args)
            replace(tmp, args.state)
    else:
        save(markov, args.output, args)