'HFGPS' is replaced by 'HFGPSRECEIVER:' to comply with section A3.2.4 of current IGC specs

[lyusupov]

There were some discrepancy is the IGC specs in past, which was explained earlier in the Issues section: https://github.com/Turbo87/aerofiles/issues/18#issue-141241207

However, it looks like IGC group has fixed that already. And most of modern FR equipment is using a complete HFGPSRECEIVER token at this time.

For details, please, take a look at page 26 of http://www.ukiws.uk/GFAC/documents/tech_spec_gnss.pdf