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/time/time.cc b/aos/time/time.cc
index 6ba9543..6a25aa9 100644
--- a/aos/time/time.cc
+++ b/aos/time/time.cc
@@ -45,8 +45,7 @@
 
 #ifdef __linux__
 
-namespace std {
-namespace this_thread {
+namespace std::this_thread {
 template <>
 void sleep_until(const ::aos::monotonic_clock::time_point &end_time) {
   struct timespec end_time_timespec;
@@ -68,8 +67,7 @@
   } while (returnval != 0);
 }
 
-}  // namespace this_thread
-}  // namespace std
+}  // namespace std::this_thread
 
 #endif  // __linux__