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/control_loops/superstructure/vacuum.cc b/y2019/control_loops/superstructure/vacuum.cc
index fda123e..a9fbd8c 100644
--- a/y2019/control_loops/superstructure/vacuum.cc
+++ b/y2019/control_loops/superstructure/vacuum.cc
@@ -7,9 +7,7 @@
 #include "y2019/control_loops/superstructure/superstructure_goal_generated.h"
 #include "y2019/control_loops/superstructure/superstructure_output_generated.h"
 
-namespace y2019 {
-namespace control_loops {
-namespace superstructure {
+namespace y2019::control_loops::superstructure {
 
 namespace chrono = ::std::chrono;
 
@@ -86,6 +84,4 @@
       monotonic_now < last_disable_has_piece_time_ + chrono::milliseconds(250);
 }
 
-}  // namespace superstructure
-}  // namespace control_loops
-}  // namespace y2019
+}  // namespace y2019::control_loops::superstructure