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.cc b/aos/events/epoll.cc
index 340d0cd..8c5c3e1 100644
--- a/aos/events/epoll.cc
+++ b/aos/events/epoll.cc
@@ -15,8 +15,7 @@
 
 #include "aos/time/time.h"
 
-namespace aos {
-namespace internal {
+namespace aos::internal {
 
 TimerFd::TimerFd()
     : fd_(timerfd_create(CLOCK_MONOTONIC, TFD_CLOEXEC | TFD_NONBLOCK)) {
@@ -298,5 +297,4 @@
       << ": Failed to " << operation << " epoll fd: " << event_data->fd;
 }
 
-}  // namespace internal
-}  // namespace aos
+}  // namespace aos::internal