path: escape spaces from `luarocks path` to work with eval

I share a home directory partition between several boot partitions on my mac, so it often looks like `/Volumes/Macintosh HD/Users/gary`, which gets truncated without this patch.  Escaping any spaces before passing to eval like this works on POSIX machines... I don't have (or want!) a Windows machine to test on, but since '\\' is the directory separator on Windows, I expect more work is needed.