Draws the feature importances as a bar chart; called from fit.

def draw(self, **kwargs):
        """
        Draws the feature importances as a bar chart; called from fit.
        """
        # Quick validation
        for param in ('feature_importances_', 'features_'):
            if not hasattr(self, param):
                raise NotFitted("missing required param '{}'".format(param))

        # Find the positions for each bar
        pos = np.arange(self.features_.shape[0]) + 0.5

        # Plot the bar chart
        if self.stack:
            colors = color_palette(kwargs.pop('colors', None),
                                   len(self.classes_))
            zeros = np.zeros(self.feature_importances_.shape[1])
            left_arr = np.zeros((self.feature_importances_.shape[1], 2))

            for idx in range(len(self.feature_importances_)):
                left = [
                    left_arr[j, int(self.feature_importances_[idx][j] > 0)]
                    for j in range(len(self.feature_importances_[idx]))
                ]

                self.ax.barh(pos, self.feature_importances_[idx], left=left,
                             color=colors[idx], label=self.classes_[idx])

                left_arr[:, 0] += np.minimum(self.feature_importances_[idx],
                                             zeros)
                left_arr[:, 1] += np.maximum(self.feature_importances_[idx],
                                             zeros)
        else:
            self.ax.barh(pos, self.feature_importances_, align='center')

        # Set the labels for the bars
        self.ax.set_yticks(pos)
        self.ax.set_yticklabels(self.features_)

        return self.ax