Update Doxygen link in iBeacon.md

Replace nonexistent class transclusion with .h file link, so build works.

Author: Amanda Butler

docs/api/bluetooth/iBeacon.md

@@ -8,7 +8,7 @@ The iBeacon class builds an advertising payload mimicking an iBeacon and assigns
 
 ### iBeacon class reference
 
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/mbed-os-api-doxy/classi_beacon.html)
+[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/mbed-os/development/mbed-os-api-doxy/i_beacon_8h_source.html)
 
 ### iBeacon example