update fix-vf-meta
update fix-vf-meta

This script has been rewritten based on feedback
provided by Thomas Linard in the following comment:
https://github.com/google/fonts/issues/2391#issuecomment-599691522

He has also reviewed the output of this updated script and has
confirmed that the fonts are working correctly.

googlefonts/gftools,googlefonts/gftools