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/frc971/vision/media_device.cc b/frc971/vision/media_device.cc
index a369cfb..46f3419 100644
--- a/frc971/vision/media_device.cc
+++ b/frc971/vision/media_device.cc
@@ -20,8 +20,7 @@
 #include "aos/scoped/scoped_fd.h"
 #include "aos/util/file.h"
 
-namespace frc971 {
-namespace vision {
+namespace frc971::vision {
 
 void Entity::Log() const {
   LOG(INFO) << "  { \"id\": " << id() << ",";
@@ -408,5 +407,4 @@
   }
 }
 
-}  // namespace vision
-}  // namespace frc971
+}  // namespace frc971::vision