Renders the class prediction error across the axis.

def draw(self):
        """
        Renders the class prediction error across the axis.
        """

        indices = np.arange(len(self.classes_))
        prev = np.zeros(len(self.classes_))

        colors = resolve_colors(
            colors=self.colors,
            n_colors=len(self.classes_))

        for idx, row in enumerate(self.predictions_):
            self.ax.bar(indices, row, label=self.classes_[idx],
                        bottom=prev, color=colors[idx])
            prev += row

        return self.ax