subcommand specifying an "argument :arg" does not display the subcommand help

[StupidCodeFactory]

When running the following i was expecting to see the print_arg full help section:

thor subcommand_with_argument help print_arg

instead i see the subcommand general help (also notice the ARG between help and [COMMAND] seems odd):

Commands:
       thor subcommand_with_argument help ARG [COMMAND]  # Describe subcommands or one specific subcommand
       thor subcommand_with_argument print_arg ARG       # My method with a cool argument

if i remove the argument in the subclass (i.e comment out this line https://github.com/StupidCodeFactory/thor/pull/1/files#diff-a113f9bffbf7327e2f860433311b4e15R11) then it does show the print_arg full help section

I've added a spec to prove my issue StupidCodeFactory#1

It's not very clear if this behaviour is erroneous, i'd like to confirm this is an issue before digging deeper into this.

Thanks guys!