doc: confusing language in util.format() docs
https://github.com/nodejs/node/commit/214d02040e1c46b8cac47451bf2f0e2fc15a3e0f
The intention to speed up util.format breaks the following case:
util.format('%%')
prior to this commit, this returned '%', now it returns '%%'.
Imho, this is a bug and should be reverted.