Update visitors.yml

Author: wangc168

_data/members/visitors.yml

@@ -1,5 +1,5 @@
 - name: "[Changchang Sun](https://scholar.google.com/citations?user=bCxWjjYAAAAJ&hl=en) (Visiting)"
-  info: Ph.D. student, Department of Computer Science, University of Illinois Chicago 
+  info: Ph.D., Department of Computer Science, University of Illinois Chicago 
   visiting: Aug. 2023 - May. 2025
   research: "<a href='https://arxiv.org/abs/2412.16780'>Forget Vectors at Play: Universal Input Perturbations Driving Machine Unlearning in Image Classification</a>"