Fix typo in to_string(int type)

[Ordoviz]

@mmd-osm commented on Apr 16, 2020:

Yes, https://github.com/drolbr/Overpass-API/blob/oversized_backend_objects/src/overpass_api/statements/query.h#L103 is incorrect. Care to create a new issue for it?
You shouldn't notice this when running a query, that method is only called when converting queries between different formats: