build test suite for `/players` API endpoint

[MarchandMD]

• Currently, there is no test suite for the /players endpoint
• Jest and SuperTest have been installed
• Test the endpoints for accuracy
  • GET /players
  • GET /players/:id
  • POST /players
  • PATCH /players/:id
  • DELETE /players/:id

(could be broken into multiple user stories)

[l-e-u]

You may assign it to me, I'm just waiting for type issue #55 to be merged, then I can tackle this one.