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/vision/extrinsics_calibration.cc b/frc971/vision/extrinsics_calibration.cc
index 9459c84..6017258 100644
--- a/frc971/vision/extrinsics_calibration.cc
+++ b/frc971/vision/extrinsics_calibration.cc
@@ -14,8 +14,7 @@
 #include "frc971/vision/charuco_lib.h"
 #include "frc971/vision/visualize_robot.h"
 
-namespace frc971 {
-namespace vision {
+namespace frc971::vision {
 
 namespace chrono = std::chrono;
 using aos::distributed_clock;
@@ -1008,5 +1007,4 @@
   filter.Visualize(calibration_parameters);
 }
 
-}  // namespace vision
-}  // namespace frc971
+}  // namespace frc971::vision