05_ticket_v2/09_error_trait: update instructions

[Sh099078]

Follow-up of https://github.com/mainmatter/100-exercises-to-learn-rust/pull/13 in the solutions branch.

[tredontho]

I know it's somewhat unrelated, but I also noticed that the solution tests don't pass

---- tests::display_is_correctly_implemented stdout ----
thread 'tests::display_is_correctly_implemented' panicked at exercises/05_ticket_v2/09_error_trait/src/lib.rs:121:9:
assertion `left == right` failed
  left: "Title error: Title cannot be empty"
 right: "Title cannot be empty"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace


failures:
    tests::display_is_correctly_implemented

I can create a separate PR if you think it would be inappropriate to include with this one, just figured I would mention because I noticed the same issues you're fixing here when working through the exercises.

[Sh099078]

Both are typos in either a comment or in a string literal of the same file. I would suggest that you do another PR since the required changes are independent from one another. Correct me if I am wrong and you would rather have them merged the next time @LukeMathWalker

[LukeMathWalker]

This has been fixed, thanks for raising the issue 👍🏻