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/util/wrapping_counter.cc b/aos/util/wrapping_counter.cc
index f98d7e3..ead4781 100644
--- a/aos/util/wrapping_counter.cc
+++ b/aos/util/wrapping_counter.cc
@@ -1,7 +1,6 @@
 #include "aos/util/wrapping_counter.h"
 
-namespace aos {
-namespace util {
+namespace aos::util {
 
 WrappingCounter::WrappingCounter(int32_t initial_count)
     : count_(initial_count), last_count_(0) {}
@@ -15,5 +14,4 @@
   return count_;
 }
 
-}  // namespace util
-}  // namespace aos
+}  // namespace aos::util