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/epoll_test.cc b/aos/events/epoll_test.cc
index b725747..e1be563 100644
--- a/aos/events/epoll_test.cc
+++ b/aos/events/epoll_test.cc
@@ -6,9 +6,7 @@
 #include "glog/logging.h"
 #include "gtest/gtest.h"
 
-namespace aos {
-namespace internal {
-namespace testing {
+namespace aos::internal::testing {
 
 // A simple wrapper around both ends of a pipe along with some helpers to easily
 // read/write data through it.
@@ -204,6 +202,4 @@
   epoll_.Run();
 }
 
-}  // namespace testing
-}  // namespace internal
-}  // namespace aos
+}  // namespace aos::internal::testing