Nest some more namespaces

Did someone previously suggest that all namespace had been
nested?  Silly.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I22278c1caaeba8b47dc46fb2ed3078c20a11e190
diff --git a/y2019/control_loops/drivetrain/localizer.h b/y2019/control_loops/drivetrain/localizer.h
index 2e7c3a5..f4c7a8a 100644
--- a/y2019/control_loops/drivetrain/localizer.h
+++ b/y2019/control_loops/drivetrain/localizer.h
@@ -17,8 +17,7 @@
 #pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
 #endif
 
-namespace y2019 {
-namespace control_loops {
+namespace y2019::control_loops {
 
 template <int num_cameras, int num_targets, int num_obstacles,
           int max_targets_per_frame, typename Scalar = double>
@@ -576,7 +575,6 @@
 #pragma GCC diagnostic pop
 #endif
 
-}  // namespace control_loops
-}  // namespace y2019
+}  // namespace y2019::control_loops
 
 #endif  // Y2019_CONTROL_LOOPS_DRIVETRAIN_LOCALIZATER_H_