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/motors/fet12/motor_controls.cc b/motors/fet12/motor_controls.cc
index 0ef7e3c..adc1839 100644
--- a/motors/fet12/motor_controls.cc
+++ b/motors/fet12/motor_controls.cc
@@ -2,8 +2,7 @@
 
 #include "motors/peripheral/configuration.h"
 
-namespace frc971 {
-namespace motors {
+namespace frc971::motors {
 namespace {
 
 template <int kRows, int kCols>
@@ -245,5 +244,4 @@
   return debug_[theta];
 }
 
-}  // namespace motors
-}  // namespace frc971
+}  // namespace frc971::motors