text: Title: Tensorflow 2.0 parallel_model problem 
  Body: I'm trying to use mrcnn today but i had this problem. 
  do you have an idea for the solution ? 
  
  ```
  model = modellib.MaskRCNN(mode="training", config=config, model_dir=args.logs)
    File "/hdd-raid0/home_server/houssem/anaconda3/envs/hxf_env/lib/python3.7/site-packages/mask_rcnn-2.1-py3.7.egg/mrcnn/model.py", line 1835, in __init__
    File "/hdd-raid0/home_server/houssem/anaconda3/envs/hxf_env/lib/python3.7/site-packages/mask_rcnn-2.1-py3.7.egg/mrcnn/model.py", line 2060, in build
    File "/hdd-raid0/home_server/houssem/anaconda3/envs/hxf_env/lib/python3.7/site-packages/mask_rcnn-2.1-py3.7.egg/mrcnn/parallel_model.py", line 37, in __init__
    File "/hdd-raid0/home_server/houssem/anaconda3/envs/hxf_env/lib/python3.7/site-packages/mask_rcnn-2.1-py3.7.egg/mrcnn/parallel_model.py", line 79, in make_parallel
    File "/hdd-raid0/home_server/houssem/anaconda3/envs/hxf_env/lib/python3.7/site-packages/mask_rcnn-2.1-py3.7.egg/mrcnn/parallel_model.py", line 79, in <listcomp>
    File "/hdd-raid0/home_server/houssem/anaconda3/envs/hxf_env/lib/python3.7/site-packages/keras/engine/base_layer.py", line 443, in __call__
      previous_mask = _collect_previous_mask(inputs)
    File "/hdd-raid0/home_server/houssem/anaconda3/envs/hxf_env/lib/python3.7/site-packages/keras/engine/base_layer.py", line 1311, in _collect_previous_mask
      mask = node.output_masks[tensor_index]
  AttributeError: 'Node' object has no attribute 'output_masks' 
  ```