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/peripheral/spi.cc b/motors/peripheral/spi.cc
index 8c4ad11..59ff651 100644
--- a/motors/peripheral/spi.cc
+++ b/motors/peripheral/spi.cc
@@ -4,8 +4,7 @@
 
 #include "motors/core/time.h"
 
-namespace frc971 {
-namespace teensy {
+namespace frc971::teensy {
 
 Spi::~Spi() {
   DisableTransmitInterrupt();
@@ -136,5 +135,4 @@
   return true;
 }
 
-}  // namespace teensy
-}  // namespace frc971
+}  // namespace frc971::teensy