fix(*): fix 18.04 complie warning.

samples/save_single_image.cc

@@ -1,4 +1,16 @@
-#include <stdio.h>
+// Copyright 2018 Slightech Co., Ltd. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
 #include <opencv2/highgui/highgui.hpp>
 
 #include "mynteye/api/api.h"