The Migrations API is the GitHub equivalent of Google TakeOut.
It allows you to create an archive of one or more repositories
that you can download and later use for import purposes.

See: https://help.github.com/enterprise/2.4/admin/guides/migrations/exporting-the-github-com-organization-s-repositories/
for more information.

Fixes #292.

Change-Id: Id20624acb4f16a2aade9143e723c8eb85ec75402