Nest some more namespaces

Did someone previously suggest that all namespace had been
nested?  Silly.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I22278c1caaeba8b47dc46fb2ed3078c20a11e190
diff --git a/y2019/vision/image_writer.h b/y2019/vision/image_writer.h
index 1192368..27dcb4a 100644
--- a/y2019/vision/image_writer.h
+++ b/y2019/vision/image_writer.h
@@ -5,8 +5,7 @@
 
 #include "aos/vision/image/image_types.h"
 
-namespace y2019 {
-namespace vision {
+namespace y2019::vision {
 
 class ImageWriter {
  public:
@@ -23,7 +22,6 @@
   unsigned int image_count_ = 0;
 };
 
-}  // namespace vision
-}  // namespace y2019
+}  // namespace y2019::vision
 
 #endif  // Y2019_VISION_IMAGE_WRITER_H_