Update username_password_sample.py

Author: rayluo

sample/username_password_sample.py

@@ -61,4 +61,4 @@
     print(result.get("correlation_id"))  # You may need this when reporting a bug
     if 65001 in result.get("error_codes", []):  # Not mean to be coded programatically, but...
         # AAD requires user consent for U/P flow
-        print("Visit this to consent:", app.get_authorization_request_url(scope))
+        print("Visit this to consent:", app.get_authorization_request_url(config["scope"]))