Issues setting background color in Python 3

[taylorbell57]

With Python 3.5.2 and matplotlib version 2.2.2, I get an error saying that there is no ax.set_axis_bgcolor function. Apparently this has been deprecated since matplotlib 2.0 (https://matplotlib.org/2.1.2/api/_as_gen/matplotlib.axes.Axes.set_axis_bgcolor.html). As a result, all instances of "set_axis_bgcolor" should be changed to "set_facecolor" throughout the script plot.py