Nest some more namespaces

Did someone previously suggest that all namespace had been
nested?  Silly.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I22278c1caaeba8b47dc46fb2ed3078c20a11e190
diff --git a/y2022/vision/blob_detector.h b/y2022/vision/blob_detector.h
index a60316a..93bba09 100644
--- a/y2022/vision/blob_detector.h
+++ b/y2022/vision/blob_detector.h
@@ -4,8 +4,7 @@
 #include <opencv2/features2d.hpp>
 #include <opencv2/imgproc.hpp>
 
-namespace y2022 {
-namespace vision {
+namespace y2022::vision {
 
 class BlobDetector {
  public:
@@ -52,7 +51,6 @@
 
   static void ExtractBlobs(cv::Mat bgr_image, BlobResult *blob_result);
 };
-}  // namespace vision
-}  // namespace y2022
+}  // namespace y2022::vision
 
 #endif  // Y2022_BLOB_DETECTOR_H_