Headings from `integration-foot` don't appear in the right-nav TOC

[sanscontext]

I think this is probably something to do with the order in which we build out the page and generate the right-nav TOC but I'm not sure.

Visible on http://segment-docs-stage.s3-website-us-west-2.amazonaws.com/docs/connections/destinations/catalog/evergage/

[sanscontext]

This isn't a stop-ship issue, just filing it for now.