emphasise the flask debug mode would stop error and transactions (#1903)

Author: Camilleli

docs/flask.asciidoc

@@ -75,8 +75,8 @@ apm = ElasticAPM(app, service_name='<APP-ID>', secret_token='<SECRET-TOKEN>')
 [[flask-debug-mode]]
 ===== Debug mode
 
-Please note that errors and transactions will only be sent to the APM Server if your app is *not* in
-http://flask.pocoo.org/docs/0.12/quickstart/#debug-mode[debug mode].
+NOTE: Please note that errors and transactions will only be sent to the APM Server if your app is *not* in
+http://flask.pocoo.org/docs/2.3.x/quickstart/#debug-mode[Flask debug mode].
 
 To force the agent to send data while the app is in debug mode,
 set the value of `DEBUG` in the `ELASTIC_APM` dictionary to `True`: