feat(cli): Add dig compatible error exit code 9

This patch implements the error exit code for "No reply from server"
that dig uses to indicate that it was unable to resolve an address due
to the inability to reach any resolver.

References:
https://linux.die.net/man/1/dig

cmd/doggo/cli.go

@@ -148,16 +148,25 @@ func main() {
 	}
 
 	// Resolve Queries.
-	var responses []resolvers.Response
+	var (
+			responses []resolvers.Response
+			responseErrors []error
+	)
 	for _, q := range app.Questions {
 		for _, rslv := range app.Resolvers {
 			resp, err := rslv.Lookup(q)
 			if err != nil {
 				app.Logger.WithError(err).Error("error looking up DNS records")
+				responseErrors = append(responseErrors, err)
 			}
 			responses = append(responses, resp)
 		}
 	}
+
+	if len(responses) == 0 && len(responseErrors) > 0 {
+		app.Logger.Exit(9)
+	}
+
 	app.Output(responses)
 
 	// Quitting.