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/blob/disjoint_set.h b/aos/vision/blob/disjoint_set.h
index 38cca1d..6343e9f 100644
--- a/aos/vision/blob/disjoint_set.h
+++ b/aos/vision/blob/disjoint_set.h
@@ -3,8 +3,7 @@
 
 #include <vector>
 
-namespace aos {
-namespace vision {
+namespace aos::vision {
 
 // Disjoint set algorithm, which is similar to what this class does:
 // https://en.wikipedia.org/wiki/Disjoint-set_data_structure
@@ -40,7 +39,6 @@
   std::vector<int> nodes_;
 };
 
-}  // namespace vision
-}  // namespace aos
+}  // namespace aos::vision
 
 #endif  // _AOS_VISION_BLOB_DISJOINT_SET_H_