Swapping ghostscript with export_fig

Hi!

I have the "usual" transparancy issue with export_fig and ghostscript

https://github.com/altmany/export_fig/issues/285

ot the advice to downgrade ghostscript to 9.28 go get around the issue. Installed it, then did the mistake of typing:

user_string('ghostscript', 'C:\Program Files\gs\gs9.28')

And now it doesn't work at all. How do I reset, or tell export_fig which ghostscript version to use? I assume that the path I used is the wrong one, it should point to something else but I have no idea which subfolder or file that I should point at....