app.py: default to DPM++ 2M Karras

app.py

@@ -229,7 +229,7 @@ with gr.Blocks(css=css) as demo:
                     with gr.Tab("Generation"):
                         with gr.Row():
                             with gr.Column(scale=1):
-                                sampler = gr.Dropdown(value="Euler a", show_label=True, label="Sampling Method", choices=prodia_client.list_samplers())
+                                sampler = gr.Dropdown(value="DPM++ 2M Karras", show_label=True, label="Sampling Method", choices=prodia_client.list_samplers())
                                 
                             with gr.Column(scale=1):
                                 steps = gr.Slider(label="Sampling Steps", minimum=1, maximum=30, value=25, step=1)