Nest some more namespaces

Did someone previously suggest that all namespace had been
nested?  Silly.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I22278c1caaeba8b47dc46fb2ed3078c20a11e190
diff --git a/frc971/vision/calibration_accumulator.h b/frc971/vision/calibration_accumulator.h
index 9a6f483..550b691 100644
--- a/frc971/vision/calibration_accumulator.h
+++ b/frc971/vision/calibration_accumulator.h
@@ -12,8 +12,7 @@
 #include "frc971/vision/foxglove_image_converter_lib.h"
 #include "frc971/wpilib/imu_batch_generated.h"
 
-namespace frc971 {
-namespace vision {
+namespace frc971::vision {
 
 // This class provides an interface for an application to be notified of all
 // camera and IMU samples in order with the correct timestamps.
@@ -143,7 +142,6 @@
   frc971::IMUValuesT last_value_;
 };
 
-}  // namespace vision
-}  // namespace frc971
+}  // namespace frc971::vision
 
 #endif  // FRC971_VISION_CALIBRATION_ACCUMULATOR_H_