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/image/image_stream.cc b/aos/vision/image/image_stream.cc
index 62f5e81..fe42efc 100644
--- a/aos/vision/image/image_stream.cc
+++ b/aos/vision/image/image_stream.cc
@@ -2,8 +2,7 @@
 
 #include "aos/logging/logging.h"
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 void ImageStreamEvent::ProcessHelper(
     DataRef data, aos::monotonic_clock::time_point timestamp) {
@@ -14,5 +13,4 @@
   ProcessImage(data, timestamp);
 }
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision