Multiprocessing error on ``DisplayCAL.multiprocess``

[eoyilmaz]

Traceback (most recent call last):
  File "/home/erkan.yilmaz/PycharmProjects/DisplayCAL/venv/lib/python3.9/site-packages/wx/lib/delayedresult.py", line 267, in wrapper
    result = workerFn(*args, **kwargs)
  File "/home/erkan.yilmaz/PycharmProjects/DisplayCAL/venv/lib/python3.9/site-packages/DisplayCAL/worker.py", line 1837, in __call__
    result = self.producer(*args, **kwargs)
  File "/home/erkan.yilmaz/PycharmProjects/DisplayCAL/venv/lib/python3.9/site-packages/DisplayCAL/worker.py", line 11320, in create_profile
    table.apply_black_offset(
  File "/home/erkan.yilmaz/PycharmProjects/DisplayCAL/venv/lib/python3.9/site-packages/DisplayCAL/ICCProfile.py", line 3183, in apply_black_offset
    self._apply_black(XYZbp, False, False, logfile, thread_abort, abortmessage)
  File "/home/erkan.yilmaz/PycharmProjects/DisplayCAL/venv/lib/python3.9/site-packages/DisplayCAL/ICCProfile.py", line 3254, in _apply_black
    pool_slice(
  File "/home/erkan.yilmaz/PycharmProjects/DisplayCAL/venv/lib/python3.9/site-packages/DisplayCAL/multiprocess.py", line 155, in pool_slice
    pool = Pool(num_workers)
  File "/usr/lib/python3.9/multiprocessing/pool.py", line 212, in __init__
    self._repopulate_pool()
  File "/usr/lib/python3.9/multiprocessing/pool.py", line 303, in _repopulate_pool
    return self._repopulate_pool_static(self._ctx, self.Process,
  File "/usr/lib/python3.9/multiprocessing/pool.py", line 319, in _repopulate_pool_static
    w = Process(ctx, target=worker,
  File "/usr/lib/python3.9/multiprocessing/process.py", line 83, in __init__
    assert group is None, 'group argument must be None for now'
AssertionError: group argument must be None for now

According to this MR nipy/nipype#2754 the Process is now a function after Python 3.7, apply a similar patch to make it work.