Option to disable keep alive for JSON-RPC http transport (#9848)

* Keep alive jsonrpc CLI option.

* Update to latest json-rpc.

* Keep alive flag.

rpc/src/tests/rpc.rs

@@ -40,6 +40,7 @@ fn serve(handler: Option<MetaIoHandler<Metadata>>) -> Server<HttpServer> {
 		},
 		1,
 		5,
+		false,
 	).unwrap())
 }