def scroll(self):
        self._start_line += 1
helper function for draw_tree using pydot
dataset/ETHPy150Open peterbrittain/asciimatics/asciimatics/screen.py/_AbstractCanvas.scroll--crossover with--dataset/ETHPy150Open balajiln/mondrianforest/src/mondrianforest.py/MondrianTree.get_print_label_draw_tree