max and min of bool to return bool like numpy

[ajpotts]

max and min functions on pdarrays of type bool should return bool to better align with numpy:

In [7]: pda = ak.zeros(size, dtype=dtype)

In [8]: ak.max(pda)
Out[8]: 0

In [9]: type(ak.max(pda))
Out[9]: numpy.int64

In [10]: type(np.max(pda.to_ndarray()))
Out[10]: numpy.bool_