example: use proto message Get methods in helloworld (#2990)

diff --git a/examples/helloworld/greeter_client/main.go b/examples/helloworld/greeter_client/main.go
index 4330b9e..f908170 100644
--- a/examples/helloworld/greeter_client/main.go
+++ b/examples/helloworld/greeter_client/main.go
@@ -54,5 +54,5 @@
 	if err != nil {
 		log.Fatalf("could not greet: %v", err)
 	}
-	log.Printf("Greeting: %s", r.Message)
+	log.Printf("Greeting: %s", r.GetMessage())
 }
diff --git a/examples/helloworld/greeter_server/main.go b/examples/helloworld/greeter_server/main.go
index e99fb26..eac8645 100644
--- a/examples/helloworld/greeter_server/main.go
+++ b/examples/helloworld/greeter_server/main.go
@@ -39,8 +39,8 @@
 
 // SayHello implements helloworld.GreeterServer
 func (s *server) SayHello(ctx context.Context, in *pb.HelloRequest) (*pb.HelloReply, error) {
-	log.Printf("Received: %v", in.Name)
-	return &pb.HelloReply{Message: "Hello " + in.Name}, nil
+	log.Printf("Received: %v", in.GetName())
+	return &pb.HelloReply{Message: "Hello " + in.GetName()}, nil
 }
 
 func main() {