Replace all lines matching `old_line` with `new_line`.

        If ``once`` is set to True, remove only the first instance.

def update(self, old_line, new_line, once=False):
        """Replace all lines matching `old_line` with `new_line`.

        If ``once`` is set to True, remove only the first instance.
        """
        nb = 0
        for block in self.blocks:
            nb += block.update(old_line, new_line, once=once)
            if nb and once:
                return nb
        return nb