update video link

Author: shihusi

_lectures/07_normalizing_flow_and_score-based_model.md

@@ -11,7 +11,7 @@ links:
 #       name: codes
     - url: /static_files/ppt/lec7-mar-31-watermark.pdf
       name: slides
-    - url: https://www.bilibili.com/video/BV1DQ5jzXES7/?share_source=copy_web&vd_source=1ef9b25809c21469eadae98f1bab39ea
+    - url: https://www.bilibili.com/video/BV156dRY8E9g/?share_source=copy_web&vd_source=1ef9b25809c21469eadae98f1bab39ea
       name: public version video
 ---