doc: Updated Bluetooth Core Spec Link

Updated the link for the Bluetooth Core Specification so that it points
to the 6.0 revision instead of the 5.4

Signed-off-by: Johansen, Thomas <[email protected]>

Author: thomas-m-johansen

doc/links.txt

@@ -85,7 +85,7 @@
 
 .. _`NMEA report sample`: http://aprs.gids.nl/nmea/#gsa
 
-.. _`Bluetooth Core Specification`: https://www.bluetooth.com/specifications/specs/core-specification-5-4/
+.. _`Bluetooth Core Specification`: https://www.bluetooth.com/specifications/specs/core-specification-6-0/
 
 .. _`Bluetooth Specifications and Documents`: https://www.bluetooth.com/specifications/specs/