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/y2018/actors/autonomous_actor.cc b/y2018/actors/autonomous_actor.cc
index ea9daab..ae017b5 100644
--- a/y2018/actors/autonomous_actor.cc
+++ b/y2018/actors/autonomous_actor.cc
@@ -8,8 +8,7 @@
 #include "aos/util/phased_loop.h"
 #include "y2018/control_loops/drivetrain/drivetrain_base.h"
 
-namespace y2018 {
-namespace actors {
+namespace y2018::actors {
 using ::frc971::ProfileParametersT;
 
 using ::aos::monotonic_clock;
@@ -599,5 +598,4 @@
   return false;
 }
 
-}  // namespace actors
-}  // namespace y2018
+}  // namespace y2018::actors