Let's Unify the naming convention with snake case( folder )

[Doppon]

I think in ruby, it use snake case for file name and folder name too.

ref: https://www.rubydoc.info/gems/rubocop/RuboCop/Cop/Naming/FileName

[Doppon]

I created the pull request.

#62

[vzvu3k6k]

Solved by #62 🎉