Where it's relevant, replace the occurrences of https://github.com/rmccue/Requests

[JustinyAhin]

As the repository has been moved under WordPress organization, it would make sense to replace some occurrences of https://github.com/rmccue/Requests in the documentation where it is relevant to do so.

Obviously these links are still working, but for consistence, it would make sense to have https://github.com/WordPress/Requests for some of them.