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/find_blob.cc b/aos/vision/blob/find_blob.cc
index ab65e34..8ee8e92 100644
--- a/aos/vision/blob/find_blob.cc
+++ b/aos/vision/blob/find_blob.cc
@@ -2,8 +2,7 @@
 
 #include "aos/vision/blob/disjoint_set.h"
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 struct BlobBuilder {
   BlobBuilder(int i) : min_y(i) {}
@@ -173,5 +172,4 @@
   return blob_set.MoveBlobs();
 }
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision