Can not use multiply gpus for bottom-up feature extraction

[Wangt-CN]

Hi, Thanks for authors great doker environment for bu feature extraction. However, I find it cannot use the multiply GPUs by using CUDA_VISIBLE_DEVICES=0,1,2,3 in docker？ And I check the extract.py file, it seemed that it does not support the multiply gpu extracting?

Or am I missing anything? Thanks~