When a user has concealed their membership in an organisation the Org.member() method does not work correctly

In this case, Github returned a 302 Found with a redirection to the public_membership resource, however, the fact that the 302 was returned as opposed to a 404 is enough to indicate membership (when membership is concealed, the redirected URL will return a 404). When the user is not a member of an org, GitHub will return a 404 immediately.

Please let me know if you want me to rework this in any way.