It's what gitsh does too: https://github.com/thoughtbot/gitsh/blob/master/man/man1/gitsh.1#L10

This happened because mdocml is a unix tool, and unix only uses short options (`-V`), but long options (`--version`) are a GNU extension, so the `-` hack works around this.

OS X is a big mix of unix and GNU, so choose whatever feels right.

More on historical precedent:
http://www.delorie.com/gnu/docs/GNU/standards_18.html
http://programmers.stackexchange.com/questions/70357/command-line-options-style-posix-or-what