append.

$ gometalinter --vendor --disable-all --enable=megacheck --disable=gotype --deadline=6m ./...
pkg/tsdb/elasticsearch/client/search_request.go:59:4:warning: should replace loop with sr.Aggs = append(sr.Aggs, aggArray...) (S1011) (megacheck)
pkg/tsdb/elasticsearch/client/search_request.go:303:4:warning: should replace loop with agg.Aggregation.Aggs = append(agg.Aggregation.Aggs, childAggs...) (S1011) (megacheck)