Add spacex-api to the clients list

[tbprojects]

Hi, I've implemented a JavaScript / TypeScript wrapper for r-spacex/SpaceX-API. Maybe it would be useful to add it to the list of the clients: https://github.com/r-spacex/SpaceX-API/blob/master/docs/clients.md

npm: https://www.npmjs.com/package/spacex-api
github: https://github.com/tbprojects/spacex-api

[jakewmeyer]

Added. Thanks!