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/hybrid_ekf.h b/frc971/control_loops/drivetrain/hybrid_ekf.h
index 743e494..f784f2e 100644
--- a/frc971/control_loops/drivetrain/hybrid_ekf.h
+++ b/frc971/control_loops/drivetrain/hybrid_ekf.h
@@ -12,17 +12,11 @@
 #include "frc971/control_loops/drivetrain/drivetrain_config.h"
 #include "frc971/control_loops/runge_kutta.h"
 
-namespace y2019 {
-namespace control_loops {
-namespace testing {
+namespace y2019::control_loops::testing {
 class ParameterizedLocalizerTest;
-}  // namespace testing
-}  // namespace control_loops
-}  // namespace y2019
+}  // namespace y2019::control_loops::testing
 
-namespace frc971 {
-namespace control_loops {
-namespace drivetrain {
+namespace frc971::control_loops::drivetrain {
 
 namespace testing {
 class HybridEkfTest;
@@ -934,8 +928,6 @@
   P_.setZero();
 }
 
-}  // namespace drivetrain
-}  // namespace control_loops
-}  // namespace frc971
+}  // namespace frc971::control_loops::drivetrain
 
 #endif  // FRC971_CONTROL_LOOPS_DRIVETRAIN_HYBRID_EKF_H_