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/y2016/vision/stereo_geometry.h b/y2016/vision/stereo_geometry.h
index c18abc5..e2ed92e 100644
--- a/y2016/vision/stereo_geometry.h
+++ b/y2016/vision/stereo_geometry.h
@@ -7,8 +7,7 @@
 #include "aos/vision/math/vector.h"
 #include "y2016/vision/calibration.pb.h"
 
-namespace y2016 {
-namespace vision {
+namespace y2016::vision {
 
 // Returns the contents of the calibration file which are embedded into the
 // code.
@@ -61,7 +60,6 @@
   Calibration calibration_;
 };
 
-}  // namespace vision
-}  // namespace y2016
+}  // namespace y2016::vision
 
 #endif  // Y2016_VISION_STEREO_GEOMETRY_H_