Fix anchors links in maven page

What does this MR do?

From the output of: https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/397, I learned some links in this EE-only page were broken.

This fixes that.

Related issues

Relates to: https://gitlab.com/gitlab-com/gitlab-docs/merge_requests/397.

Author's checklist

• Apply the correct labels and milestone

Review checklist

• Technical writer's review (required)