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/tcp-source.cc b/aos/vision/debug/tcp-source.cc
index de406ae..7749f5c 100644
--- a/aos/vision/debug/tcp-source.cc
+++ b/aos/vision/debug/tcp-source.cc
@@ -12,8 +12,7 @@
 #include "aos/vision/debug/debug_framework.h"
 #include "aos/vision/events/tcp_client.h"
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 // Reads packets in the form:
 // uint32 length
@@ -152,5 +151,4 @@
 
 REGISTER_IMAGE_SOURCE("tcp", TCPImageSource);
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision