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/y2016/vision/target_sender.cc b/y2016/vision/target_sender.cc
index a0a0dc7..5a842b7 100644
--- a/y2016/vision/target_sender.cc
+++ b/y2016/vision/target_sender.cc
@@ -18,8 +18,7 @@
 #include "y2016/vision/stereo_geometry.h"
 #include "y2016/vision/vision_data.pb.h"
 
-namespace y2016 {
-namespace vision {
+namespace y2016::vision {
 using aos::events::DataSocket;
 using aos::events::TCPServer;
 using aos::events::TXUdpSocket;
@@ -218,8 +217,7 @@
   loop.Run();
 }
 
-}  // namespace vision
-}  // namespace y2016
+}  // namespace y2016::vision
 
 int main(int, char **) {
   using namespace y2016::vision;