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/sensor_reader.cc b/frc971/wpilib/sensor_reader.cc
index 1486042..447e3b4 100644
--- a/frc971/wpilib/sensor_reader.cc
+++ b/frc971/wpilib/sensor_reader.cc
@@ -17,8 +17,7 @@
 DEFINE_int32(pwm_offset, 5050 / 2,
              "Offset of reading the sensors from the start of the PWM cycle");
 
-namespace frc971 {
-namespace wpilib {
+namespace frc971::wpilib {
 
 SensorReader::SensorReader(::aos::ShmEventLoop *event_loop)
     : event_loop_(event_loop),
@@ -180,5 +179,4 @@
   }
 }
 
-}  // namespace wpilib
-}  // namespace frc971
+}  // namespace frc971::wpilib