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/aos/vision/debug/overlay.h b/aos/vision/debug/overlay.h
index a2cecd5..3beb9e1 100644
--- a/aos/vision/debug/overlay.h
+++ b/aos/vision/debug/overlay.h
@@ -8,8 +8,7 @@
 #include "aos/vision/math/segment.h"
 #include "aos/vision/math/vector.h"
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 // Abstract away rendering to avoid compiling gtk for arm.
 // This should match a reduced cairo rendering api.
@@ -239,7 +238,6 @@
   std::vector<std::pair<Vector<2>, double>> circles_;
 };
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision
 
 #endif  // _AOS_VISION_IMAGE_DEBUG_OVERLAY_H_