Converting python plugin-in shellout.py from gimp 2.x to 3.x

[Neptunus]

Hi iiey,

I uninstalled version 3.0.0 of GIMP and installed version 3.0.2.
The nik collection works without any new action. Nikplugin is ailready at the right place.

Many thanks for what you did !
Best regards,
Neptunus