上傳base64圖片，獲取圖片MD5
base64圖片轉換
//base64轉化ArrayBuffer再SparkMD5
function _base64ToArrayBufferToMD5(base64) {
const buffer = uni.base64ToArrayBuffer(base64)
var spark = new SparkMD5.ArrayBuffer();
spark.append(buffer);
var hexHash = spark.end(false);
return hexHash;
}