missed reference in /examples/greeter/srv /main.go

[blueeyezhy]

There might be an wrong reference in /examples/greeter/srv /main.go, which cause err in go mod tidy.

Line.10: "go-micro.dev/v4/util/log" => log "go-micro.dev/v4/logger"
Line.17: log.Log("Received Say.Hello request") => log.Log(0, "Received Say.Hello request")