Replace Doxygen link in HeartRateService.md

Replace transclusion with .h file because class page doesn't exist anymore and is breaking the build.

Author: Amanda Butler

docs/api/bluetooth/HeartRateService.md

@@ -10,7 +10,7 @@ The HeartRateService class implements the Bluetooth Heart Rate service as define
 
 ### HeartRateService class reference
 
-[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/development/mbed-os-api-doxy/class_heart_rate_service.html)
+[![View code](https://www.mbed.com/embed/?type=library)](https://os.mbed.com/docs/mbed-os/development/mbed-os-api-doxy/_heart_rate_service_8h_source.html)
 
 ### HeartRateService example