A return value typo error of print_trading_env()
function (livr -> live) is modified.
inherits(orders, "data.frame") condition is added to
kis_cancel_all() function, because the
get_orders() function inside of
kis_cancel_all() function returns a list of error code if
the class of return value is not a data.frame. So if
get_orders() function returns a list of error code, the
print_trading_env() function returns the same list of error
code.