Doc for `iff` is wrong

[rudolph9]

https://hooks-common.feathersjs.com/hooks.html#iff

Says the third argument is the hookFuncsFalse but is actually treated as chained additional hook to invoke in true case.

It looks like this actually describing the args for iffElse.

[silvestreh]

Docs seem to be outdated. The Migrating page seems to imply that Version 5.0.0 is the latest and/or there are no breaking changes since 5.x.

[fratzinger]

Fixed via #766