Let's use attr_accessor

[asiniy]

Even though it's not a functional change, I find these small syntax fixing more readable

Fixes # .

Changes:

Please ensure that:

• [ ] Changelog is updated if not a minor patch
• [ ] Ruby linting is ok: rubocop is all green
• [ ] Javascript linting is ok: cd javascript/webpacker_react-npm-module/ && yarn lint is all green
• [ ] Tests are all green