Ch6: Subclass/Superclass confusion for `Ord`/`Eq`

In Ch6, in section `Ord`, it is stated that [«Eq is a subclass of Ord»](https://github.com/purescript-contrib/purescript-book/blob/master/text/chapter6.md?plain=1#L167). However, in the section on Superclasses, it is stated that [«the `Eq` class is a superclass of `Ord` [...]»](https://github.com/purescript-contrib/purescript-book/blob/874eefeb4b9c6635bec5021ef59fdf8d0038978b/text/chapter6.md?plain=1#L602C72-L602C76).