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/y2019/vision/debug_serial.cc b/y2019/vision/debug_serial.cc
index 9b88260..79849b9 100644
--- a/y2019/vision/debug_serial.cc
+++ b/y2019/vision/debug_serial.cc
@@ -13,8 +13,7 @@
 #include "y2019/jevois/structures.h"
 #include "y2019/jevois/uart.h"
 
-namespace y2019 {
-namespace vision {
+namespace y2019::vision {
 
 void main(int argc, char **argv) {
   (void)argc;
@@ -85,7 +84,6 @@
   }
 }
 
-}  // namespace vision
-}  // namespace y2019
+}  // namespace y2019::vision
 
 int main(int argc, char **argv) { y2019::vision::main(argc, argv); }