project 3.2: edition2021 bug

[pnkfelix]

Was walking through project 03.02 and hit this:

(.venv) Admin:~/environment/Lesson03/project02 (master) $ cargo +nightly build --release --out-dir=./my-example-function/out -Z unstable-options --manifest-path ./my-example-function/Cargo.toml
error: failed to parse manifest at `/home/ec2-user/environment/Lesson03/project02/my-example-function/Cargo.toml`

Caused by:
  feature `edition2021` is required

  The package requires the Cargo feature called `edition2021`, but that feature is not stabilized in this version of Cargo (1.56.0-nightly (cc17afbb0 2021-08-02)).
  Consider adding `cargo-features = ["edition2021"]` to the top of Cargo.toml (above the [package] table) to tell Cargo you are opting in to use this unstable feature.
  See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#edition-2021 for more information about the status of this feature.