Fix incorrect source in 16.1

[boojongmin]

10 | drop(v); // oh no!
   | ^ value used here after move

In the book, I should get a compilation error, but the source now passes compilation.

This pull request modifies the example source to produce compilation errors consistent with the book.

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(This image captures that part.)

[anemochore]

Which Rust version are you using? What is your OS and IDE? Listing 16-3 won't compile on Rust 1.74.1 (current stable).

[boojongmin]

close. this was an invalid pull request.