Fix testing bug

[PeganovAnton]

If the rightmost painted cell has to be on the border of the robot pitch
the cell is not painted and task testing system reports an error wrongly.

Если крайняя клетка, которую нужно закрасить, на границе, тестирующая система ее не включает в задание.

[PeganovAnton]

Мое решение к задаче

#!/usr/bin/python3

from pyrob.api import *


def cell_needs_filling(cell_idx, filled_idx):
    return 2 * cell_idx == filled_idx * (filled_idx - 1)


@task
def task_7_5():
    """Consider arithmetic progression with initial term `a_1 = 0`
    and difference `d = 1`. Distance between `n`-th painted cell 
    (counting from one) and first painted cell is equal to 
    sum of first `n` members of the progression. Here the distance
    is the difference between row indices of the painted cells.
    
    Consider a robot passing through `n-1` painted cells and stopping
    exactly before `n`-th painted cell (`n = 1, ...`). 
    Let the `k` be number steps made by the robot (`k = 0, ...`). 
    Than, in consideration of position of the first painted cell, `k` 
    and `n` satisfy the following equation
    `k = n * (n-1) / 2` (follows from formula of sum of first members
    of arithmetic progression).   
    
    """
    cell_idx = 0
    filled_idx = 1
    while not wall_is_on_the_right():
        move_right()
        if cell_needs_filling(cell_idx, filled_idx):
            fill_cell()
            filled_idx += 1
        cell_idx += 1


if __name__ == '__main__':
    run_tasks()

[fufler]

Спасибо за PR. Нужно поправить решение , чтобы сборка проходила корректно.