NotFound when deleting repo hooks

[nateberkopec]

github_client.repos.hooks.list(repo: "foo", user: "bar").each do |h|                                                              
  github_client.repos.hooks.delete(repo: "foo", user: "bar", id: h.id)                                                            
end                                                                                                                                                       
# Github::Error::NotFound: DELETE

This looks superficially similar to #170