update set_axis_bg_color depricated in matplotlib 2.0

itten/visuals.py

@@ -59,7 +59,7 @@ class SequencePlot(object):
         axt.xaxis.set_major_locator(loc)
         axt.xaxis.set_major_formatter(fmt)
 
-        ax.set_axis_bgcolor((1, 1, 1))  # TODO: gradient
+        ax.set_facecolor((1, 1, 1))  # INFO war vor matplotlib 2 set_axis_bgcolor
 
         chn_label = view._contrast
         ax.set_ylabel(chn_label, {'fontsize': 8})