[JOSS Review] Link to FORTRAN implementation is not working

[santisoler]

While reading the README.md I noticed that the link to Tsoulis' FORTRAN implementation is not working. At least I cannot access that code. Is this the right url? Or this is a problem on the SEG? I'm referring to this line:

polyhedral-gravity-model/README.md

Line 55 in ebe47ec

and its corresponding [implementation in FORTRAN](https://software.seg.org/2012/0001/index.html).

This is not a major concern, but I decided to open this Issue it so you are aware.

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This issue is part of the JOSS review: openjournals/joss-reviews#6384

[schuhmaj]

For me, as well, the link does not work anymore. Thank you for letting me know.

I will leave this issue open for now. Maybe the site will return in a few days/ weeks. Otherwise, I remove the broken link.

[santisoler]

Sounds good. FIY, this issue will not block the publication of the JOSS article. I just wanted to let you know that the link is broken.