fix: show 2 dashes on help for single digit option key or alias

[mleguen]

To be coherent with what yargs/parser considers as an option single dash key, do not display '-1' but '--1' when '1' is used as an option key or an alias.

See #1454

[bcoe]

This seems reasonable to me, I remembered this legitimate use of --100:

https://node-tap.org/docs/coverage/100/

[bcoe]

fixes: #1454

[ruyadorno]

@bcoe heads up this changes does not quite fits the example you gave of --100 since it's checking for a single-digit only...

...and unfortunately it breaks the help page for one of my modules that uses the -0 standard, similar to xargs:

XARGS(1)                  BSD General Commands Manual                 XARGS(1)

NAME
     xargs -- construct argument list(s) and execute utility

SYNOPSIS
     xargs [-0opt] [-E eofstr] [-I replstr [-R replacements]] [-J replstr] [-L number] [-n number [-x]] [-P maxprocs]
           [-s size] [utility [argument ...]]

DESCRIPTION
     The xargs utility reads space, tab, newline and end-of-file delimited strings from the standard input and exe-
     cutes utility with the strings as arguments.

     [... redacted for brevity]

     The options are as follows:

     -0      Change xargs to expect NUL (``\0'') characters as separators, instead of spaces and newlines.  This is
             expected to be used in concert with the -print0 function in find(1).

[ruyadorno]

I ended up figuring out that yargs-parser itself does not have support to such pattern (which surprises me given its popularity within some of the day-to-day tools I use)

I gave it a try at actually implementing support to it in the parser but not really sure how that will go 😬 yargs/yargs-parser#255 - if it eventually makes its way into the parser then we also should update lib/usage.js to match it