Moduledoc: Always add newline

[zimt28]

The only inconsistency I could spot after installing styler are (non-)empty lines after the moduledoc. It would be nice if an empty line could be enforced, as this seems more common (in the Elixir lang codebase).

[novaugust]

thanks zimt! i noticed that too recently and kind of scratched my head as to why every other directive block gets a newline after it but moduledoc doesn't...
someone else noticing it means i'll likely change it up then. appreciate you making an issue

[ethunk]

I took a stab at creating a branch to fix or address this issue. #243