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/realtime_test.cc b/aos/realtime_test.cc
index 97f21c8..348489b 100644
--- a/aos/realtime_test.cc
+++ b/aos/realtime_test.cc
@@ -8,8 +8,7 @@
 
 DECLARE_bool(die_on_malloc);
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 
 // Tests that ScopedRealtime handles the simple case.
 TEST(RealtimeTest, ScopedRealtime) {
@@ -133,8 +132,7 @@
 
 #endif
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing
 
 // We need a special gtest main to force die_on_malloc support on.  Otherwise
 // we can't test CHECK statements before turning die_on_malloc on globally.