R package updates mess with output

[mccarthy-m-g]

The GitHub actions runner currently uses the most recent releases of the R packages I'm using to write the book. However, my local machine is using earlier versions as I update infrequently. This leads to discrepancies in output between my computer and the GitHub actions runner. I should decide whether to restrict what package versions can be used by the GitHub actions runner, or whether to update my computer's R packages more frequently.

I noticed this with my most recent push, as now Fig 1.1 in the preface is messed up in the web build.