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/ADIS16448.cc b/frc971/wpilib/ADIS16448.cc
index 597c5e8..c8aadfd 100644
--- a/frc971/wpilib/ADIS16448.cc
+++ b/frc971/wpilib/ADIS16448.cc
@@ -11,8 +11,7 @@
 #include "aos/time/time.h"
 #include "frc971/wpilib/imu_generated.h"
 
-namespace frc971 {
-namespace wpilib {
+namespace frc971::wpilib {
 
 using ::aos::monotonic_clock;
 namespace chrono = ::std::chrono;
@@ -424,5 +423,4 @@
   return true;
 }
 
-}  // namespace wpilib
-}  // namespace frc971
+}  // namespace frc971::wpilib