text: Title: VOT Testing AssertionError: 
  Body: I created VOT2018 folder and put VOT2018.json file inside, To do a quick check I run 
  
  >> python -u ../../tools/test.py \
          --snapshot snapshot/checkpoint_e5.pth \
  	--config config.yaml \	--dataset VOT2018 2>&1 | tee logs/test_dataset.log
  
  And got this error. 
  
  >>AssertionError: /home/thomas/pysot/tools/../testing_dataset/VOT2018/ants1/color/00000001.jpg
  loading VOT2018:   0%|                                                    | 0/60 [00:00<?, ?it/s, ants1]
  
  What is problem? Do I need to download VOT2018 (images) datset and put it inside VOT2018 folder?  I found out pysot-toolkit, but did not get it properly,  how to download VOT2018 datset? 