message: Update changelog note about crate-versions flag.
diff: - Added new feature resolver.
  [#7820](https://github.com/rust-lang/cargo/pull/7820)
  - Rustdoc docs now automatically include the version of the package in the
  - side bar.
  + side bar (requires `-Z crate-versions` flag).
  [#7903](https://github.com/rust-lang/cargo/pull/7903)
  ## Cargo 1.42 (2020-03-12)
  