Ported changes for GetAllContributors from IRepositoriesClient to IObservableRepositoriesClient
Merge pull request #624 from gabrielweyer/GetAllContributors-observable-fix

CheckObservableClients is failing
run the convention tests to ensure we keep everything in sync
no verbose plz
Merge pull request #629 from octokit/add-back-convention-tests

run the convention tests to ensure we keep everything in sync