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/y2019/vision/constants.h b/y2019/vision/constants.h
index 959f5b7..7078d6b 100644
--- a/y2019/vision/constants.h
+++ b/y2019/vision/constants.h
@@ -6,8 +6,7 @@
 #include <cstdint>
 #include <string>
 
-namespace y2019 {
-namespace vision {
+namespace y2019::vision {
 
 // Position of the idealized camera in 3d space.
 struct CameraGeometry {
@@ -107,7 +106,6 @@
 void DumpCameraConstants(const char *fname, int camera_id,
                          const CameraCalibration &value);
 
-}  // namespace vision
-}  // namespace y2019
+}  // namespace y2019::vision
 
 #endif  // _Y2019_VISION_CONSTANTS_H_