Breadcrumbs in Readthedocs theme

[tommy-hartmann]

In the readthedocs theme the breadcrumbs for mkapi in pagemode are not correctly displayed.
The line before API should not be displayed. I think that is a problem with the page.anchestors for the mkapi pages.

Steps to reproduce:

• in mkdocs.yaml set:

   theme:
    name: readthedocs

• build / serve the doc: mkdocs serve
• open url in browser, e.g. http://localhost:8000/api/mkapi.core.attribute/