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/y2017/actors/autonomous_actor.cc b/y2017/actors/autonomous_actor.cc
index 19aa329..f67f0d7 100644
--- a/y2017/actors/autonomous_actor.cc
+++ b/y2017/actors/autonomous_actor.cc
@@ -8,8 +8,7 @@
 #include "aos/util/phased_loop.h"
 #include "y2017/control_loops/drivetrain/drivetrain_base.h"
 
-namespace y2017 {
-namespace actors {
+namespace y2017::actors {
 using ::aos::monotonic_clock;
 using ::frc971::ProfileParametersT;
 namespace chrono = ::std::chrono;
@@ -321,5 +320,4 @@
   return true;
 }
 
-}  // namespace actors
-}  // namespace y2017
+}  // namespace y2017::actors