Fix failing tests on windows

[vfdev-5]

🐛 Bug description

 tests\ignite\contrib\metrics\test_precision_recall_curve.py:4: in <module>
    from sklearn.metrics import precision_recall_curve
c:\miniconda3\envs\test\lib\site-packages\sklearn\__init__.py:80: in <module>
    from .base import clone
c:\miniconda3\envs\test\lib\site-packages\sklearn\base.py:21: in <module>
    from .utils import _IS_32BIT
c:\miniconda3\envs\test\lib\site-packages\sklearn\utils\__init__.py:20: in <module>
    from scipy.sparse import issparse
c:\miniconda3\envs\test\lib\site-packages\scipy\__init__.py:104: in <module>
    from . import _distributor_init
c:\miniconda3\envs\test\lib\site-packages\scipy\_distributor_init.py:61: in <module>
    WinDLL(os.path.abspath(filename))
c:\miniconda3\envs\test\lib\ctypes\__init__.py:364: in __init__
    self._handle = _dlopen(self._name, mode)
E   OSError: [WinError 126] The specified module could not be found

Related to scipy/scipy#12400

A fix can be downgrading scipy to 1.4.1.

Environment

• PyTorch Version (e.g., 1.4):
• Ignite Version (e.g., 0.3.0):
• OS (e.g., Linux):
• How you installed Ignite (conda, pip, source):
• Python version:
• Any other relevant information: