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/y2020/control_loops/drivetrain/drivetrain_base.h b/y2020/control_loops/drivetrain/drivetrain_base.h
index e35c2af..321e7cc 100644
--- a/y2020/control_loops/drivetrain/drivetrain_base.h
+++ b/y2020/control_loops/drivetrain/drivetrain_base.h
@@ -3,15 +3,11 @@
 
 #include "frc971/control_loops/drivetrain/drivetrain_config.h"
 
-namespace y2020 {
-namespace control_loops {
-namespace drivetrain {
+namespace y2020::control_loops::drivetrain {
 
 const ::frc971::control_loops::drivetrain::DrivetrainConfig<double> &
 GetDrivetrainConfig();
 
-}  // namespace drivetrain
-}  // namespace control_loops
-}  // namespace y2020
+}  // namespace y2020::control_loops::drivetrain
 
 #endif  // y2020_CONTROL_LOOPS_DRIVETRAIN_DRIVETRAIN_BASE_H_