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/aos/vision/image/image_dataset.h b/aos/vision/image/image_dataset.h
index 7801cec..10ea13e 100644
--- a/aos/vision/image/image_dataset.h
+++ b/aos/vision/image/image_dataset.h
@@ -4,8 +4,7 @@
 #include <string>
 #include <vector>
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 struct DatasetFrame {
   // TODO: These should be V4L formats ideally.
@@ -17,7 +16,6 @@
 
 DatasetFrame LoadFile(const std::string &jpeg_filename);
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision
 
 #endif  // _AOS_VISION_IMAGE_IMAGE_DATASET_H_