Add setting change captcha height

[gandriyko]

Add possible to change the ratio of height
Now this multiplier is hardcoded to 1.2

 size = (size[0] * 2, int(size[1] * 1.2))

Full code

def captcha_image(request, key, scale=1):
    store = get_object_or_404(CaptchaStore, hashkey=key)
    text = store.challenge

    if settings.CAPTCHA_FONT_PATH.lower().strip().endswith('ttf'):
        font = ImageFont.truetype(settings.CAPTCHA_FONT_PATH, settings.CAPTCHA_FONT_SIZE * scale)
    else:
        font = ImageFont.load(settings.CAPTCHA_FONT_PATH)

    size = font.getsize(text)
    size = (size[0] * 2, int(size[1] * 1.2))