fix mask.py

[kentaroy47]

fix for #410

will work if you have cocoapi installed.

[kentaroy47]

similar to unmerged PR in #466, but there were a lot of unnecessary changes there.

[EMCP]

this actually did not work... with a blank fresh copy of the project I am seeing

(pytorch1_py37_tut) emcp@emcp-corei7-2600k:/media/latest_mount/Dev/git/jwyang/faster-rcnn.pytorch$ vim lib/pycocotools/mask.py 
(pytorch1_py37_tut) emcp@emcp-corei7-2600k:/media/latest_mount/Dev/git/jwyang/faster-rcnn.pytorch$ python trainval_net.py --net res101 --dataset pascal_voc --cuda --bs 2 
Traceback (most recent call last):
  File "trainval_net.py", line 27, in <module>
    from roi_data_layer.roidb import combined_roidb
  File "/media/latest_mount/Dev/git/jwyang/faster-rcnn.pytorch/lib/roi_data_layer/roidb.py", line 9, in <module>
    from datasets.factory import get_imdb
  File "/media/latest_mount/Dev/git/jwyang/faster-rcnn.pytorch/lib/datasets/factory.py", line 15, in <module>
    from datasets.coco import coco
  File "/media/latest_mount/Dev/git/jwyang/faster-rcnn.pytorch/lib/datasets/coco.py", line 23, in <module>
    from pycocotools.coco import COCO
  File "/media/latest_mount/Dev/git/jwyang/faster-rcnn.pytorch/lib/pycocotools/coco.py", line 60, in <module>
    from . import mask
  File "/media/latest_mount/Dev/git/jwyang/faster-rcnn.pytorch/lib/pycocotools/mask.py", line 3, in <module>
    from pycocotools._mask import _mask
ModuleNotFoundError: No module named 'pycocotools._mask'

[EMCP]

similar to unmerged PR in #466, but there were a lot of unnecessary changes there.

those updates brought the latest version into the project.. and it worked when I performed it.

[kentaroy47]

@EMCP
Thanks for pointing this out.
Yes, i found it doesn't work.. let me look into this.

(another quick workaround is commenting out import mask in the script if you're just doing binding box detection..)