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/frc971/control_loops/drivetrain/spline.cc b/frc971/control_loops/drivetrain/spline.cc
index 609d3b1..a7f749e 100644
--- a/frc971/control_loops/drivetrain/spline.cc
+++ b/frc971/control_loops/drivetrain/spline.cc
@@ -1,8 +1,6 @@
 #include "frc971/control_loops/drivetrain/spline.h"
 
-namespace frc971 {
-namespace control_loops {
-namespace drivetrain {
+namespace frc971::control_loops::drivetrain {
 
 ::Eigen::Matrix<double, 2, 6> Spline4To6(
     const ::Eigen::Matrix<double, 2, 4> &control_points) {
@@ -36,6 +34,4 @@
   return new_control_points;
 }
 
-}  // namespace drivetrain
-}  // namespace control_loops
-}  // namespace frc971
+}  // namespace frc971::control_loops::drivetrain