follow guideline
follow guideline

`mix new` no longer generates a `config/config.exs`

SEE ALSO:

- https://hexdocs.pm/elixir/library-guidelines.html#avoid-application-configuration
- https://github.com/elixir-lang/elixir/blob/v1.9/CHANGELOG.md#configuration-overhaul

ma2gedev/breadcrumble_ex