app.py: fix typo

app.py

@@ -36,7 +36,7 @@ class Prodia:
         response = self._get(f"{self.base}/sdxl/models")
         return response.json()
 
-    def list_samplers(seflf):
+    def list_samplers(self):
         response = self._get(f"{self.base}/sdxl/samplers")
         return response.json()