doc: fix "timout" typo in timeout

Corrected to `timeout`

PR-URL: https://github.com/nodejs/node/pull/8231


Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Yorkie Liu <yorkiefixer@gmail.com>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>