Move from direct iframe embed to embed api

Use the :sparkles: GeoJSON Embed API :sparkles: endpoint to embed the map rather than directly embedding the underlying iframe.

*Note: realize this is a pull request to the compiled branch, but it looks like [the post doesn't exist in the `source` branch](https://github.com/geobabbler/geobabbler.github.com/tree/source).*

**Edit:** May also make sense to update the [Instructions](https://help.github.com/articles/mapping-geojson-files-on-github#embedding-your-map-elsewhere) in the post?