fixed log format

internal/mock/grpc_server.go

@@ -127,7 +127,7 @@ func StartGrpcServer() *grpc.Server {
 
 	lis, err := net.Listen("tcp", fmt.Sprintf(":%d", GrpcMockPort))
 	if err != nil {
-		log.Fatal("gRPC server failed to listen: %v", err)
+		log.Fatal(fmt.Sprintf("gRPC server failed to listen: %v", err))
 	}
 
 	log.Info(fmt.Sprintf("gRPC server listening on port %d", GrpcMockPort))