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/y2018/vision/vision_status.cc b/y2018/vision/vision_status.cc
index ef3fd5a..ec5ea55 100644
--- a/y2018/vision/vision_status.cc
+++ b/y2018/vision/vision_status.cc
@@ -8,8 +8,7 @@
 #include "y2018/vision.pb.h"
 #include "y2018/vision/vision_generated.h"
 
-namespace y2018 {
-namespace vision {
+namespace y2018::vision {
 
 using aos::monotonic_clock;
 
@@ -43,8 +42,7 @@
   }
 }
 
-}  // namespace vision
-}  // namespace y2018
+}  // namespace y2018::vision
 
 int main(int argc, char **argv) {
   ::aos::InitGoogle(&argc, &argv);