message: Don't mention current ResolveVersion in comment
diff: @@ -46,8 +46,10 @@ pub struct Resolve {
  summaries: HashMap<PackageId, Summary>,
  }
  -/// A version to indicate how a `Cargo.lock` should be serialized. Currently
  -/// [V3 is the default](ResolveVersion::default) when creating a new lockfile.
  +/// A version to indicate how a `Cargo.lock` should be serialized.
  +///
  +/// When creating a new lockfile, the default version defined in
  +/// [`ResolveVersion::default`] is used.
  /// If an old version of lockfile already exists, it will stay as-is.
  ///
  /// It's theorized that we can add more here over time to track larger changes
  