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/testing/test_logging_test.cc b/aos/testing/test_logging_test.cc
index f39c6cf..5731545 100644
--- a/aos/testing/test_logging_test.cc
+++ b/aos/testing/test_logging_test.cc
@@ -6,8 +6,7 @@
 
 #include "aos/logging/logging.h"
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 
 // Tests logging from multiple threads.
 // tsan used to complain about this.
@@ -25,5 +24,4 @@
   thread.join();
 }
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing