Replace all '9koXpg98eAheJpvBs5tK' occurrences with '<your_access_token>' in API docs.
This new endpoint allow users to update a submodule's reference. The MR involves adding a new operation RPC operation in gitaly-proto (see gitlab-org/gitaly-proto!233) and change Gitaly to use this new version (see gitlab-org/gitaly!936). See gitlab-org/gitlab-ce!20949