Nest some more namespaces

Did someone previously suggest that all namespace had been
nested?  Silly.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I22278c1caaeba8b47dc46fb2ed3078c20a11e190
diff --git a/aos/time/time.h b/aos/time/time.h
index cd4ecda..1a5cbd1 100644
--- a/aos/time/time.h
+++ b/aos/time/time.h
@@ -118,15 +118,13 @@
 
 #ifdef __linux__
 
-namespace std {
-namespace this_thread {
+namespace std::this_thread {
 // Template specialization for monotonic_clock, since we can use clock_nanosleep
 // with TIMER_ABSTIME and get very precise absolute time sleeps.
 template <>
 void sleep_until(const ::aos::monotonic_clock::time_point &end_time);
 
-}  // namespace this_thread
-}  // namespace std
+}  // namespace std::this_thread
 
 #endif  // __linux__