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/polytope_test.cc b/frc971/control_loops/polytope_test.cc
index 0a01248..542c981 100644
--- a/frc971/control_loops/polytope_test.cc
+++ b/frc971/control_loops/polytope_test.cc
@@ -8,8 +8,7 @@
 
 #include "aos/testing/test_logging.h"
 
-namespace frc971 {
-namespace controls {
+namespace frc971::controls {
 
 class HPolytopeTest : public ::testing::Test {
  protected:
@@ -102,5 +101,4 @@
               .finished())));
 }
 
-}  // namespace controls
-}  // namespace frc971
+}  // namespace frc971::controls