examples: semiring: add a newline to the fixup file
examples: semiring: add a newline to the fixup file

Otherwise we get something like this:

```
let (int_semiring : unit -> (unit, unit) FStar_Tactics_Effect.tac_repr) =
  fun uu___ -> canon_semiring int_crlet _ =
  FStar_Tactics_Native.register_tactic "CanonCommSemiring.canon_semiring_aux"
```

since the extracted file does not have a newline at the end.

FStarLang/FStar,FStarLang/FStar,FStarLang/FStar