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/frc971/control_loops/drivetrain/localizer.h b/frc971/control_loops/drivetrain/localizer.h
index 867b3c0..6f5bf3d 100644
--- a/frc971/control_loops/drivetrain/localizer.h
+++ b/frc971/control_loops/drivetrain/localizer.h
@@ -7,9 +7,7 @@
 #include "frc971/control_loops/drivetrain/hybrid_ekf.h"
 #include "frc971/control_loops/pose.h"
 
-namespace frc971 {
-namespace control_loops {
-namespace drivetrain {
+namespace frc971::control_loops::drivetrain {
 
 // An interface for target selection. This provides an object that will take in
 // state updates and then determine what poes we should be driving to.
@@ -214,8 +212,6 @@
   TrivialTargetSelector target_selector_;
 };
 
-}  // namespace drivetrain
-}  // namespace control_loops
-}  // namespace frc971
+}  // namespace frc971::control_loops::drivetrain
 
 #endif  // FRC971_CONTROL_LOOPS_DRIVETRAIN_FIELD_ESTIMATOR_H_