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/y2017/vision/target_sender.cc b/y2017/vision/target_sender.cc
index a198cd2..1e6e049 100644
--- a/y2017/vision/target_sender.cc
+++ b/y2017/vision/target_sender.cc
@@ -27,8 +27,7 @@
 #include "y2017/vision/vision_config.pb.h"
 #include "y2017/vision/vision_result.pb.h"
 
-namespace y2017 {
-namespace vision {
+namespace y2017::vision {
 
 using aos::events::DataSocket;
 using aos::events::TCPServer;
@@ -215,8 +214,7 @@
   return true;
 }
 
-}  // namespace vision
-}  // namespace y2017
+}  // namespace y2017::vision
 
 int main(int, char **) {
   using namespace y2017::vision;