IGRF update

[C. Philippe Escoubet]

There is a new igrf.d version created by Mike Hapgood at JSOC that extrapolate to 2024. I would suggest using this one in the next release. It can be found at: http://www.jsoc.rl.ac.uk/pub/ovt/

[Erik Johansson]

igrf.d has been updated with the suggested file which contains data for 1980-2020, where 2020 is extrapolated data.

A better future long-term solution would be to look at how OVT extrapolates IGRF data itself and when it gives warnings.