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/viewer.cc b/y2020/vision/viewer.cc
index ff08f01..8ba2955 100644
--- a/y2020/vision/viewer.cc
+++ b/y2020/vision/viewer.cc
@@ -20,8 +20,7 @@
 DEFINE_string(capture, "",
               "If set, capture a single image and save it to this filename.");
 
-namespace frc971 {
-namespace vision {
+namespace frc971::vision {
 namespace {
 
 aos::Fetcher<CameraImage> image_fetcher;
@@ -170,8 +169,7 @@
 }
 
 }  // namespace
-}  // namespace vision
-}  // namespace frc971
+}  // namespace frc971::vision
 
 // Quick and lightweight grayscale viewer for images
 int main(int argc, char **argv) {