Any links on the manual page:

https://docs.mongodb.com/master/reference/geojson/

that points to http://geojson.org/geojson-spec.html needs to be updated to point to RFC 7946.
The geojson.org page already states
"This document is obsolete. Please see RFC 7946 instead."

For example, a link for GeoJSON Polygon http://geojson.org/geojson-spec.html#polygon needs to be updated to point to https://tools.ietf.org/html/rfc7946#section-3.1.6 instead.