Fix ar map

[liuwenran]

the aspect ratio map is like tthis

ASPECT_RATIO_MAP = {
    "3:8": "0.38",
    "9:21": "0.43",
    "12:25": "0.48",
    "1:2": "0.50",
    "9:17": "0.53",
    "27:50": "0.54",
    "9:16": "0.56",
    "5:8": "0.62",
    "2:3": "0.67",
    "3:4": "0.75",
    "1:1": "1.00",
    "4:3": "1.33",
    "3:2": "1.50",
    "16:9": "1.78",
    "17:9": "1.89",
    "2:1": "2.00",
    "50:27": "2.08",
}

so when I want to generate images with 1024 1:1 ar, an error comes up.