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/containers/inlined_vector_test.cc b/aos/containers/inlined_vector_test.cc
index 7368844..c9f2dd2 100644
--- a/aos/containers/inlined_vector_test.cc
+++ b/aos/containers/inlined_vector_test.cc
@@ -6,8 +6,7 @@
 
 DECLARE_bool(die_on_malloc);
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 
 // Checks that we don't malloc until/unless we need to increase the size of the
 // vector.
@@ -45,5 +44,4 @@
   zero.push_back(1);
   ASSERT_EQ(1, zero[0]);
 }
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing