Update package.json for latest version of npm
Update package.json for latest version of npm

The main module is now specified in a `main` attribute.

Signed-off-by: Ben Noordhuis <59bd0a3ff43b32849b319e645d4798d8a5d1e889@bnoordhuis.nl>

bnoordhuis/node-mmap,bnoordhuis/node-mmap,bnoordhuis/node-mmap