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/test_utils.cc b/aos/vision/blob/test_utils.cc
index 7664f8a..0e7240f 100644
--- a/aos/vision/blob/test_utils.cc
+++ b/aos/vision/blob/test_utils.cc
@@ -1,7 +1,6 @@
 #include "aos/vision/blob/test_utils.h"
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 RangeImage LoadFromTestData(int mini, const char *data) {
   // Consume initial return.
@@ -39,5 +38,4 @@
   return RangeImage(mini, std::move(rows));
 }
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision