Update for IGRF 14th generation

[MarceloBanik]

Description of the desired feature
The IGRF 14th generation was released (https://www.ngdc.noaa.gov/IAGA/vmod/coeffs/igrf14coeffs.txt)
It would be great if GMT updated their IGRF coefficients.

I implemented it after commit 6ccb32a (see git.diff.igrf14.txt) and passed the same tests before the implementation.
git.diff.igrf14.txt

Are you willing to help implement and maintain this feature? Yes/No
Yes. But I hope someone more used with the pull requests could apply the git.diff.igrf14.txt

[joa-quim]

Thanks Marcelo (I was being sloppy with this). PR #8635 is on its way to apply this patch.