Update README.md (open-mmlab#520)

fix typo

Author: jin-s13

tools/data/ucf101/README.md

@@ -34,7 +34,7 @@ bash download_videos.sh
 For better decoding speed, you can resize the original videos into smaller sized, densely encoded version by:
 
 ```
-python ../resize_videos.py ../../../data/ucf101/videos/ ../../../data/ucf101/videos_256p_dense_cache --dense --level 2 --ext avi
+python ../resize_video.py ../../../data/ucf101/videos/ ../../../data/ucf101/videos_256p_dense_cache --dense --level 2 --ext avi
 ```
 
 ## Step 3. Extract RGB and Flow