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/flatbuffers_test.cc b/aos/flatbuffers_test.cc
index 333d5d7..c4113e9 100644
--- a/aos/flatbuffers_test.cc
+++ b/aos/flatbuffers_test.cc
@@ -7,8 +7,7 @@
 #include "aos/json_to_flatbuffer_generated.h"
 #include "aos/testing/tmpdir.h"
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 
 // Tests that Verify works.
 TEST(FlatbufferTest, Verify) {
@@ -87,5 +86,4 @@
   }
 }
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing