message: Update manifest.md
  Suggestion for text when the edition isn't defined at all
diff: @@ -125,15 +125,14 @@ set to the latest edition. Setting the `edition` key in
  `[package]` will affect all targets/crates in the package, including test
  suites, benchmarks, binaries, examples, etc.
  -If the `edition` key is not set to a specific [Rust Edition] in your
  -`Cargo.toml`, Cargo will default to 2018.
  -
  ```toml
  [package]
  # ...
  edition = '2018'
  ```
  +If the `edition` key is not set in your `Cargo.toml` file, Cargo will default to 2015.
  +
  #### The `description` field
  The description is a short blurb about the package. [crates.io] will display
  