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/aos/vision/math/vector_test.cc b/aos/vision/math/vector_test.cc
index 8c5244d..214a50c 100644
--- a/aos/vision/math/vector_test.cc
+++ b/aos/vision/math/vector_test.cc
@@ -2,9 +2,7 @@
 
 #include "gtest/gtest.h"
 
-namespace aos {
-namespace vision {
-namespace testing {
+namespace aos::vision::testing {
 
 class VectorTest : public ::testing::Test {
  protected:
@@ -71,6 +69,4 @@
   EXPECT_NEAR(M_PI / 3, vec5.AngleToZero(), 0.0001);
 }
 
-}  // namespace testing
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision::testing