Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/aos/vision/debug/camera-source.cc b/aos/vision/debug/camera-source.cc
index 578ebc1..685b7eb 100644
--- a/aos/vision/debug/camera-source.cc
+++ b/aos/vision/debug/camera-source.cc
@@ -7,8 +7,7 @@
 #include "aos/vision/image/camera_params.pb.h"
 #include "aos/vision/image/image_stream.h"
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 class CameraImageSource : public ImageSource {
  public:
@@ -63,5 +62,4 @@
 
 REGISTER_IMAGE_SOURCE("camera", CameraImageSource);
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision