Docs: documentation website incorrect information about serving local assets

[daattali]

Documentation on page https://dashr.plotly.com/external-resources

1. It says that for hosting from CDN, app.scripts.config.serve_locally = False must be set, but this is incorrect and probably copy-pasted from the python docs (the syntax is even not correct)
2. In the code sample code it shows app$run_server(serve_locally = FALSE) but this is also incorrect

The correct code is Dash$new(serve_locally = FALSE)