Whenever gem not support the last day of month expression

like expression :- "55 23 L * ? *" , this expression say that "this will execute At 11:55 PM, on the last day of the month"

but this expression is not supported, when i write this on shedule.rb file it will generate error like:- /whenever-1.0.0/lib/whenever/cron.rb:150:in 'Whenever::Output::Cron#parse_as_string': Couldn't parse: "55 23 L * ? *" (ArgumentError)

    raise ArgumentError, "Couldn't parse: #{@time.inspect}"