Make map dot more visible

The OSM_GPS_MAP_SOURCE_VIRTUAL_EARTH_HYBRID shows cities as red dots
in a couple of the zoom levels.  Make the dive dots larger and
yellow to make them stand out.

Signed-off-by: Henrik Brautaset Aronsen <subsurface@henrik.synth.no>
Signed-off-by: Dirk Hohndel <dirk@hohndel.org>