fix typescript environments

[darai0512]

checks

• [ ] pass unit tests
• [ ] pass scinario test
• [ ] use require('payjp')

Refs

for typescript usage

• https://www.typescriptlang.org/docs/home.html
• https://github.com/nodejs/llhttp/tree/master/src
• https://github.com/DefinitelyTyped/DefinitelyTyped/tree/master/types/stripe