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/runge_kutta_test.cc b/frc971/control_loops/runge_kutta_test.cc
index e07c469..1022a47 100644
--- a/frc971/control_loops/runge_kutta_test.cc
+++ b/frc971/control_loops/runge_kutta_test.cc
@@ -2,9 +2,7 @@
 
 #include "gtest/gtest.h"
 
-namespace frc971 {
-namespace control_loops {
-namespace testing {
+namespace frc971::control_loops::testing {
 
 // Tests that integrating dx/dt = e^x works.
 TEST(RungeKuttaTest, Exponential) {
@@ -92,6 +90,4 @@
   EXPECT_NEAR(y1(0, 0), RungeKuttaTimeVaryingSolution(6.0)(0, 0), 1e-7);
 }
 
-}  // namespace testing
-}  // namespace control_loops
-}  // namespace frc971
+}  // namespace frc971::control_loops::testing