add test case

[AhnSeongHyun]

use travis-ci

[AhnSeongHyun]

using https://www.getpostman.com/docs/validating_json_collections

https://schema.getpostman.com/json/collection/v1/ use this collection json and valid json and creating markdown file in testcase.

[AhnSeongHyun]

https://schema.getpostman.com/

[AhnSeongHyun]

https://github.com/Plate-Project/postman2md/tree/feature/travis-ci