There was an issue openend in august 14 over at the REST API repo concerning ACF. The short answer is that ACF needs to handle this.
If you just want read ACF fields PanManAms supplied a wordpress plugin in the same thread which will add ACF field values to the REST API.
—Git Hub Issue: https://github.com/WP-API/WP-API/issues/433
—Plugin: https://github.com/PanManAms/WP-JSON-API-ACF
