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_test.cc b/motors/usb/constants_test.cc
index 4d11349..66e0ea5 100644
--- a/motors/usb/constants_test.cc
+++ b/motors/usb/constants_test.cc
@@ -2,9 +2,7 @@
 
 #include "gtest/gtest.h"
 
-namespace frc971 {
-namespace teensy {
-namespace testing {
+namespace frc971::teensy::testing {
 
 TEST(EndpointBufferStateTest, Filling) {
   EXPECT_TRUE(BufferStateHasEmpty(EndpointBufferState::kBothEmptyEvenFirst));
@@ -61,6 +59,4 @@
             BufferStateAfterEmpty(EndpointBufferState::kBothFullEvenFirst));
 }
 
-}  // namespace testing
-}  // namespace teensy
-}  // namespace frc971
+}  // namespace frc971::teensy::testing