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/y2020/vision/extrinsics_calibration.cc b/y2020/vision/extrinsics_calibration.cc
index 334de0b..deda8c3 100644
--- a/y2020/vision/extrinsics_calibration.cc
+++ b/y2020/vision/extrinsics_calibration.cc
@@ -21,8 +21,7 @@
 DEFINE_string(base_intrinsics, "",
               "Intrinsics to use for extrinsics calibration.");
 
-namespace frc971 {
-namespace vision {
+namespace frc971::vision {
 namespace chrono = std::chrono;
 using aos::distributed_clock;
 using aos::monotonic_clock;
@@ -146,8 +145,7 @@
   }
 }
 
-}  // namespace vision
-}  // namespace frc971
+}  // namespace frc971::vision
 
 int main(int argc, char **argv) {
   aos::InitGoogle(&argc, &argv);