Correct reference to Beacon v2 API

The EJP-RD VP API spec v 4.0 is compatible with the [Beacon v2 Specification](https://github.com/ga4gh-beacon/beacon-v2) but the formatting in [README.md on line 19](https://github.com/CARE-SM/beaconAPI4CARESM/blob/6e30dc6f0ac19e39be45d665b9839250dbae7a3b/README.md?plain=1#L19) makes it look like there is a 4.0 version. The latest GA4GH Beacon v2 version at the time of writing is 2.1.