fix doc

Author: magicmark

docs/code_examples/http_multipart_async.py

@@ -9,7 +9,7 @@
 
 async def main():
 
-    transport = HTTPMultipartTransport(url="http://localhost:8000/graphql")
+    transport = HTTPMultipartTransport(url="https://gql-book-server.fly.dev/graphql")
 
     # Using `async with` on the client will start a connection on the transport
     # and provide a `session` variable to execute queries on this connection