More minor cleanup

[TonyCTHsu]

1. Remove ruby versioning to generate appraisal groups
2. Remove broken rspec and cucumber dependencies for task :main

[anmarchenko]

I think this is a dependency for task :all that it should run tests for main, cucumber, and rspec

Maybe we would rather need to add minitest here?

[TonyCTHsu]

Ideally, it should include all those tasks.

However, those tasks can only been executed with proper dependencies installed (using Appraisal at this moment).

For example:
✅ bundle exec rake spec:main
🔴 bundle exec rake spec:cucumber
✅ bundle exec appraisal cucumber8 rake spec:cucumber