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/usb.cc b/motors/usb/usb.cc
index 2c64b61..e5e581b 100644
--- a/motors/usb/usb.cc
+++ b/motors/usb/usb.cc
@@ -6,8 +6,7 @@
 
 #include "motors/util.h"
 
-namespace frc971 {
-namespace teensy {
+namespace frc971::teensy {
 namespace {
 
 // The mask of interrupts we care about.
@@ -1068,5 +1067,4 @@
   *MutableBdtEntry(endpoint, direction, odd) = bdt_entry;
 }
 
-}  // namespace teensy
-}  // namespace frc971
+}  // namespace frc971::teensy