Update app.py

the argument `shouldConvert` in function `process_image` now has default value `False`.
The default value is required because at the line 91 the function is calling without second argument.

app.py

@@ -14,7 +14,7 @@ from PIL import Image
 YOUR_API_TOKEN = os.getenv('YOUR_API_TOKEN')
 dashscope.api_key = YOUR_API_TOKEN
 math_messages = []
-def process_image(image, shouldConvert):
+def process_image(image, shouldConvert=False):
     # 获取上传文件的目录
     global math_messages
     math_messages = [] # reset when upload image