Update licensing.md - fix anchors

[amureki]

Issue: #

Description

Link anchors with capital letters (like in https://opensource.zalando.com/docs/resources/licensing/#Code-licensed-under-AGPL-or-variants-thereof) are accessible in GitHub, but do not work properly on the website. While this could be solved on the code level by fixing URL dispatching logic, I am not sure I'd be able to tackle this. Simple solution for this page - to fix anchors on this page. Lowercased links both working on GitHub and on a static-generated website.

Types of Changes

What types of changes does your code introduce? remove the points which aren't applicable:

• Refactor/improvements

Checklist

Go over all the following points, and put an x in all the boxes that apply:

• [x] My change requires a change to the documentation & I have updated it accordingly.

[amureki]

Note to maintainers:

You are welcome to reopen this PR and merge it at your will. I am going to close it for now to clean up my PR list to have less distraction.