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/y2019/vision/target_finder.cc b/y2019/vision/target_finder.cc
index b59792c..7efc38a 100644
--- a/y2019/vision/target_finder.cc
+++ b/y2019/vision/target_finder.cc
@@ -6,8 +6,7 @@
 
 using namespace aos::vision;
 
-namespace y2019 {
-namespace vision {
+namespace y2019::vision {
 
 TargetFinder::TargetFinder()
     : target_template_(Target::MakeTemplate()),
@@ -632,5 +631,4 @@
   return needs_update;
 }
 
-}  // namespace vision
-}  // namespace y2019
+}  // namespace y2019::vision