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/uuid_test.cc b/aos/uuid_test.cc
index 74e7935..f6ed21e 100644
--- a/aos/uuid_test.cc
+++ b/aos/uuid_test.cc
@@ -3,8 +3,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace aos {
-namespace testing {
+namespace aos::testing {
 
 // Tests that random UUIDs are actually random, and we can convert them to a
 // string.  Not very exhaustive, but it is a good smoke test.
@@ -52,5 +51,4 @@
   EXPECT_EQ(u_span, u2);
 }
 
-}  // namespace testing
-}  // namespace aos
+}  // namespace aos::testing