Changes to bin_1D function

Earlier the bin_1D function if the nx(number of bins) is None

(if nx is None)

from

nx = core._defaults["bins"]

to:

nx = int(max_x - min_x)

Note:
  min_x : float, optional
      Left edge of first bin defaults to minimum value of x
  max_x : float, optional
      Right edge of last bin defaults to maximum value of x