update example to use local db

[edublancas]

this example is connecting to a remote database; if users download it, they won't be able to run it; so we should update it to use local data.

we can use the same data as here: https://jupysql.readthedocs.io/en/latest/compose.html

[edublancas]

looks like the build is failing: https://readthedocs.org/projects/jupysql/builds/18184333/

[RodolfoFerro]

I've opened an issue for failing builds ( #11 ), so we can close this one.