constants: errors -> errno

lib/constants.js was incorrectly copying the constants from the
binding, by copying from `contants.os.errors` instead of
`constants.os.errno`.

PR-URL: https://github.com/nodejs/node/pull/9349


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Prince John Wesley <princejohnwesley@gmail.com>
Reviewed-By: Ron Korving <ron@ronkorving.nl>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>