Update rustyline to 4.1.0 to fix nightly build

Author: sanxiyn

Cargo.lock

@@ -18,7 +18,7 @@ env_logger="0.5.10"
 clap = "2.31.2"
 rustpython_parser = {path = "parser"}
 rustpython_vm = {path = "vm"}
-rustyline = "2.1.0"
+rustyline = "4.1.0"
 xdg = "2.2.0"
 
 [dev-dependencies.cpython]