quick fix for syncing server making connection

syncing/downloader/server.go

@@ -2,7 +2,6 @@ package downloader
 
 import (
 	"context"
-	"fmt"
 	"log"
 	"net"
 
@@ -31,7 +30,9 @@ func (s *Server) Query(ctx context.Context, request *pb.DownloaderRequest) (*pb.
 
 // Start starts the Server on given ip and port.
 func (s *Server) Start(ip, port string) (*grpc.Server, error) {
-	lis, err := net.Listen("tcp", fmt.Sprintf("%s:%s", ip, port))
+	// TODO(minhdoan): Currently not using ip. Fix it later.
+	addr := net.JoinHostPort("", port)
+	lis, err := net.Listen("tcp", addr)
 	if err != nil {
 		log.Fatalf("failed to listen: %v", err)
 	}