Agile Web Development with Rails 7: Iteration F4 crashes

I’m working with Version B2.0 of the epub. After making the changes in Iteration F4, the app crashes and the console shows errors related to Redis. I dug through the provided sample code and determined the fix was as simple as updating the development section of the config/cable.yml file:

development:
  adapter: async

Nowhere in the book did I see anything that mentioned making that change.

Erik