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/aos/vision/blob/range_image.cc b/aos/vision/blob/range_image.cc
index bf8d09f..92f77cc 100644
--- a/aos/vision/blob/range_image.cc
+++ b/aos/vision/blob/range_image.cc
@@ -3,8 +3,7 @@
 #include <algorithm>
 #include <cmath>
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 namespace {
 
 // Merge sort of multiple range images into a single range image.
@@ -142,5 +141,4 @@
   return area;
 }
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision