ghi label only fetches a single page of labels.

[foxish]

The command "ghi label" only pulls only a single page of labels from a repository which is the first 30 labels. For example, https://api.github.com/repos/kubernetes/kubernetes/labels?page=1 through https://api.github.com/repos/kubernetes/kubernetes/labels?page=6 exist, but only the first page is shown by ghi.