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/c2d_test.cc b/frc971/control_loops/c2d_test.cc
index 14b4952..47a87a0 100644
--- a/frc971/control_loops/c2d_test.cc
+++ b/frc971/control_loops/c2d_test.cc
@@ -6,9 +6,7 @@
 
 #include "frc971/control_loops/runge_kutta.h"
 
-namespace frc971 {
-namespace controls {
-namespace testing {
+namespace frc971::controls::testing {
 
 class C2DTest : public ::testing::Test {
  public:
@@ -86,6 +84,4 @@
   EXPECT_LT((A_d - A_d_fast).norm(), 1e-20);
 }
 
-}  // namespace testing
-}  // namespace controls
-}  // namespace frc971
+}  // namespace frc971::controls::testing