Update FreeGpt.py

Changed older domain url with the working new url

g4f/Provider/FreeGpt.py

@@ -7,7 +7,7 @@ from ..requests import StreamSession
 from .base_provider import AsyncGeneratorProvider
 
 domains = [
-    'https://r.aifree.site'
+    'https://s.aifree.site'
 ]
 
 class FreeGpt(AsyncGeneratorProvider):
@@ -59,4 +59,4 @@ class FreeGpt(AsyncGeneratorProvider):
     
 def generate_signature(timestamp: int, message: str, secret: str = ""):
     data = f"{timestamp}:{message}:{secret}"
-    return hashlib.sha256(data.encode()).hexdigest()
+    return hashlib.sha256(data.encode()).hexdigest()