fix SyntaxError

app_base.py

@@ -35,7 +35,7 @@ def create_demo() -> gr.Blocks:
         generate_size: int,
         enhance_scale: int = 2,
         pre_upscale: bool = True,
-        upscale_prompt: str,
+        upscale_prompt: str = "a person with perfect face",
         pre_upscale_steps: int = 10,
     ):
         w2 = 1.0