`Seq.Indexed.concat` doesn't return `Seq.Indexed` with multiple collections

`Seq.Indexed().concat([1], [2]).zip()` fails with `Error: TypeError: Seq.Indexed(...).concat(...).zip is not a function` as it is not returning an `Seq.Indexed` (`ConcatSeq` is deriving from `Seq`, not `Seq.Indexed`)