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/vision/events/udp.cc b/aos/vision/events/udp.cc
index 2aaac82..cf7ad23 100644
--- a/aos/vision/events/udp.cc
+++ b/aos/vision/events/udp.cc
@@ -4,8 +4,7 @@
 
 #include "glog/logging.h"
 
-namespace aos {
-namespace events {
+namespace aos::events {
 
 TXUdpSocket::TXUdpSocket(const std::string &ip_addr, int port)
     : fd_(socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)) {
@@ -49,5 +48,4 @@
   return result;
 }
 
-}  // namespace events
-}  // namespace aos
+}  // namespace aos::events