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/zeroing/hall_effect_and_position.cc b/frc971/zeroing/hall_effect_and_position.cc
index e074668..99454e4 100644
--- a/frc971/zeroing/hall_effect_and_position.cc
+++ b/frc971/zeroing/hall_effect_and_position.cc
@@ -6,8 +6,7 @@
 
 #include "glog/logging.h"
 
-namespace frc971 {
-namespace zeroing {
+namespace frc971::zeroing {
 
 HallEffectAndPositionZeroingEstimator::HallEffectAndPositionZeroingEstimator(
     const ZeroingConstants &constants)
@@ -123,5 +122,4 @@
   return builder.Finish();
 }
 
-}  // namespace zeroing
-}  // namespace frc971
+}  // namespace frc971::zeroing