message: use impl Trait
diff: @@ -206,13 +206,10 @@ impl DepsFrame {
  .unwrap_or(0)
  }
  - pub fn flatten<'s>(&'s self) -> Box<Iterator<Item = (&PackageId, Dependency)> + 's> {
  - // TODO: with impl Trait the Box can be removed
  - Box::new(
  + pub fn flatten<'s>(&'s self) -> impl Iterator<Item=(&PackageId, Dependency)> + 's {
  self.remaining_siblings
  .clone()
  - .map(move |(_, (d, _, _))| (self.parent.package_id(), d)),
  - )
  + .map(move |(_, (d, _, _))| (self.parent.package_id(), d))
  }
  }
  