'go build .' yields this error otherwise:

  $ go build .
  go: inconsistent vendoring in /tmp/logcat:
  	github.com/olivere/elastic/v7@v7.0.19: is explicitly required in go.mod, but not marked as explicit in vendor/modules.txt

  run 'go mod vendor' to sync, or use -mod=mod or -mod=readonly to ignore the vendor directory