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/wpilib/encoder_and_potentiometer.cc b/frc971/wpilib/encoder_and_potentiometer.cc
index 578fb96..8a94e15 100644
--- a/frc971/wpilib/encoder_and_potentiometer.cc
+++ b/frc971/wpilib/encoder_and_potentiometer.cc
@@ -3,8 +3,7 @@
 #include "aos/logging/logging.h"
 #include "aos/realtime.h"
 
-namespace frc971 {
-namespace wpilib {
+namespace frc971::wpilib {
 
 bool DMAEncoder::DoUpdateFromSample(const DMASample &sample) {
   if (index_last_value_) {
@@ -20,5 +19,4 @@
   return false;
 }
 
-}  // namespace wpilib
-}  // namespace frc971
+}  // namespace frc971::wpilib