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/constants.h b/motors/usb/constants.h
index 58c9ecc..6970639 100644
--- a/motors/usb/constants.h
+++ b/motors/usb/constants.h
@@ -3,8 +3,7 @@
 
 #include <stdint.h>
 
-namespace frc971 {
-namespace teensy {
+namespace frc971::teensy {
 
 enum class Direction : uint32_t {
   kTx = 1 << 1,
@@ -108,7 +107,6 @@
                              static_cast<uint32_t>(Data01::kData1));
 }
 
-}  // namespace teensy
-}  // namespace frc971
+}  // namespace frc971::teensy
 
 #endif  // MOTORS_USB_CONSTANTS_H_