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/jevois/camera/image_stream.h b/y2019/jevois/camera/image_stream.h
index f1ab0af..5b29070 100644
--- a/y2019/jevois/camera/image_stream.h
+++ b/y2019/jevois/camera/image_stream.h
@@ -7,8 +7,7 @@
 #include "aos/vision/image/camera_params.pb.h"
 #include "y2019/jevois/camera/reader.h"
 
-namespace y2019 {
-namespace camera {
+namespace y2019::camera {
 
 // Converts a camera reader into a virtual base class that calls ProcessImage
 // on each new image.
@@ -48,7 +47,6 @@
   std::unique_ptr<Reader> reader_;
 };
 
-}  // namespace camera
-}  // namespace y2019
+}  // namespace y2019::camera
 
 #endif  // Y2019_JEVOIS_CAMERA_IMAGE_STREAM_H_