Review Requirement/SketchupRequire

[thomthom]

As of RuboCop 0.88 there is a new cop: Style/RedundantFileExtensionInRequire rubocop/rubocop#7333 & rubocop/rubocop#8272

https://docs.rubocop.org/rubocop/cops_style.html#styleredundantfileextensioninrequire

Sounds like it's doing a similar thing. Review how it works and potentially port over logic.