Hi!
That’s a new one, haven’t run into that before! I’ll revisit this tomorrow when I have more time, but in the mean-time here’s two things to try:
Option 1: Lock the revision
Change the bracket-lib dependency to =0.8.1, and then run cargo update. That will force the package to the version that was live when the book released.
Option 2: Update Rust
At your command-line, issue rustup self update and then rustup update. I’m running rustup version 1.6.3 here, which definitely includes the new resolver system.
Hope that helps!