Fix instance check

[ConnectedSystems]

Resubmitting PR.

This package does not work as expected under Windows due to differences in numpy object instance check., causing TypeError to be raised.

e.g. Under Ubuntu, Py2.7, numpy 1.14.3

>>> import numpy as np
>>> isinstance(np.int32(5), int), isinstance(np.int64(5), int)
(True, True)

Under Windows 10, Py2.7, numpy 1.14.3

>>> import numpy as np
>>> isinstance(np.int32(5), int), isinstance(np.int64(5), int)
(True, False)

Replaced base int type with Integral from the numbers package as a workaround

>>> import numpy as np
>>> from numbers import Integral
>>> isinstance(np.int32(5), Integral), isinstance(np.int64(5), Integral)
(True, True)