use skip_ps_command => 1 as getppid() will not return the right value

From Masahiro Nagano:

server-status command is nice idea, but this command can't get all process
pid, because getppid() doesn't returns plack's pid.

The code to get process pid list is in around line 147 of Lite.pm
https://github.com/kazeburo/Plack-Middleware-ServerStatus-Lite/blob/master/lib
/Plack/Middleware/ServerStatus/Lite.pm#L147

Maybe, it's required to separate scoreboard implementation from
Plack::Middleware, And required to change a way to getppid().