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/usb/interrupt_out.cc b/motors/usb/interrupt_out.cc
index 568e5c5..30f024e 100644
--- a/motors/usb/interrupt_out.cc
+++ b/motors/usb/interrupt_out.cc
@@ -1,7 +1,6 @@
 #include "motors/usb/interrupt_out.h"
 
-namespace frc971 {
-namespace teensy {
+namespace frc971::teensy {
 
 void InterruptOut::Initialize() {
   interface_ = AddInterface();
@@ -86,5 +85,4 @@
   }
 }
 
-}  // namespace teensy
-}  // namespace frc971
+}  // namespace frc971::teensy