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_test.cc b/aos/util/wrapping_counter_test.cc
index 3ef503b..17605a0 100644
--- a/aos/util/wrapping_counter_test.cc
+++ b/aos/util/wrapping_counter_test.cc
@@ -4,9 +4,7 @@
 
 #include "gtest/gtest.h"
 
-namespace aos {
-namespace util {
-namespace testing {
+namespace aos::util::testing {
 
 TEST(WrappingCounterTest, Basic) {
   WrappingCounter test_counter;
@@ -53,6 +51,4 @@
   test_wrapping(0, 255);
 }
 
-}  // namespace testing
-}  // namespace util
-}  // namespace aos
+}  // namespace aos::util::testing