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/libc/dirname.h b/aos/libc/dirname.h
index fa733d7..c549b3c 100644
--- a/aos/libc/dirname.h
+++ b/aos/libc/dirname.h
@@ -3,13 +3,11 @@
 
 #include <string>
 
-namespace aos {
-namespace libc {
+namespace aos::libc {
 
 // Thread-safe version of dirname(3).
 ::std::string Dirname(const ::std::string &path);
 
-}  // namespace libc
-}  // namespace aos
+}  // namespace aos::libc
 
 #endif  // AOS_LIBC_DIRNAME_H_