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/y2019/constants.cc b/y2019/constants.cc
index 0332252..26188de 100644
--- a/y2019/constants.cc
+++ b/y2019/constants.cc
@@ -20,8 +20,7 @@
 #include "y2019/control_loops/superstructure/wrist/integral_wrist_plant.h"
 #include "y2019/vision/constants.h"
 
-namespace y2019 {
-namespace constants {
+namespace y2019::constants {
 
 using ::frc971::zeroing::PotAndAbsoluteEncoderZeroingEstimator;
 
@@ -428,5 +427,4 @@
   }
 }
 
-}  // namespace constants
-}  // namespace y2019
+}  // namespace y2019::constants