Elasticsearch 6.7.2 warns about deprecated field _routing

When I run gitlab-elasticsearch-indexer against elasticsearch-6.7.2 it fills my log with the following warnings:

elasticsearch | [2019-07-30T13:41:26,718][WARN ][o.e.d.c.ParseField ] [OwEc-8u] Deprecated field [_routing] used, expected [routing] instead

Would be nice to get rid of these warnings