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/events/glib_main_loop_test.cc b/aos/events/glib_main_loop_test.cc
index aabab68..6fced6d 100644
--- a/aos/events/glib_main_loop_test.cc
+++ b/aos/events/glib_main_loop_test.cc
@@ -10,8 +10,7 @@
 #include "aos/events/shm_event_loop.h"
 #include "aos/testing/path.h"
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 using aos::testing::ArtifactPath;
 
 const FlatbufferDetachedBuffer<Configuration> &Config() {
@@ -128,5 +127,4 @@
   EXPECT_EQ(runs, 1);
 }
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing