Numpy histogram large tensor fix

[Zha0q1]

this pr fixes numpy histogram against large tensors

local run:

ubuntu@ip-172-31-38-169:~/workspace$ pytest tests/nightly/test_np_large_array.py::test_histogram
=================================================== test session starts ====================================================
platform linux -- Python 3.7.7, pytest-5.4.1, py-1.8.1, pluggy-0.13.1
rootdir: /home/ubuntu/workspace, inifile: pytest.ini
plugins: remotedata-0.3.2, openfiles-0.4.0, astropy-header-0.1.2, hypothesis-5.8.3, arraydiff-0.3, doctestplus-0.5.0
collected 1 item                                                                                                           

tests/nightly/test_np_large_array.py .                                                                               [100%]

===================================================== warnings summary =====================================================
tests/nightly/test_np_large_array.py:92
  /home/ubuntu/workspace/tests/nightly/test_np_large_array.py:92: DeprecationWarning: invalid escape sequence \ 
    '''

tests/nightly/test_np_large_array.py:1323
  /home/ubuntu/workspace/tests/nightly/test_np_large_array.py:1323: DeprecationWarning: invalid escape sequence \ 
    '''

-- Docs: https://docs.pytest.org/en/latest/warnings.html
============================================== 1 passed, 2 warnings in 23.46s ====================================

[mxnet-bot]

Hey @Zha0q1 , Thanks for submitting the PR
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[access2rohit]

LGTM