[Bug] in run_demo.py

[yunfuliu]

https://github.com/zhengshou/scnn/blob/master/demo/run_demo.py#L166
The "win_weight" should be changed to "window_weight" for correctly locating the .csv file.

Also, in
https://github.com/zhengshou/scnn/blob/master/demo/run_demo.py#L56
the '../lib/preprocess/ffmpeg -i ' should be changed to 'ffmpeg -i ' to use the installed ffmpeg.

[zhengshou]

Thank you Yunfu for pointing this bug out! It's fixed now.

As for ffmpeg, yeah sure, you can use 'ffmpeg -i ' directly if already installed ffmpeg. If just downloaded executable files into '../lib/preprocess/', then shall use '../lib/preprocess/ffmpeg -i '.