Reduce packed gem size (#973)
Reduce packed gem size (#973)

This change aims to reduce the packed gem size by removing needless files from `s.files`.

Also, `s.test_files` is also removed because it is not defined in the gemspec reference.
(see <https://guides.rubygems.org/specification-reference/>)

- Size changed: 215K -> 264K
- Files changed: 221 files -> 120 files
stripe/stripe-ruby