doc: address use of profanity in code of conduct

PR-URL: https://github.com/nodejs/node/pull/3827


Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Julien Gilli <jgilli@fastmail.fm>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Alexis Campailla <alexis@janeasystems.com>