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/visualize_robot_sample.cc b/frc971/vision/visualize_robot_sample.cc
index 6ca7a9c..ad1d6b6 100644
--- a/frc971/vision/visualize_robot_sample.cc
+++ b/frc971/vision/visualize_robot_sample.cc
@@ -14,8 +14,7 @@
 #include "aos/time/time.h"
 #include "frc971/vision/visualize_robot.h"
 
-namespace frc971 {
-namespace vision {
+namespace frc971::vision {
 
 // Show / test the basics of visualizing the robot frames
 void Main(int /*argc*/, char ** /* argv */) {
@@ -45,8 +44,7 @@
   cv::imshow("Display", image_mat);
   cv::waitKey();
 }
-}  // namespace vision
-}  // namespace frc971
+}  // namespace frc971::vision
 
 int main(int argc, char **argv) {
   aos::InitGoogle(&argc, &argv);