Bug in draw_vline()

I think there is a little bug in `draw_vline()`.
You check for boundaries like this:
```python
if self.is_off_grid(x, y, x, y + h):
```
But shouldn't ist be this:
```python
if self.is_off_grid(x, y, x, y + h - 1):
```
Like it is in `draw_hline()`:
```python
if self.is_off_grid(x, y, x + w - 1, y):
```

Just wanted to let you know