Fix sectioning in Chapter 4?

[ryantmoore]

In the 2022 tidyverse of QSS, section 4.3 is only a single paragraph. This paragraph is part of a larger section in the non-tidy original version. Maybe 4.4 should be a subsection, e.g.?

[kosukeimai]

Oh yes, that's a typo. Not sure if we can fix it at this point, but I will check with the publisher.