I've got the same problem unfortunately... When i try to install the extension from the .zip file with Aseprite beta 1.2beta12, i get the following error message:
(I'm on Mac OS X Sierra)
That's very weird, I'm going to send this as a bug report to David and will get back to you guys soon, thanks.
Updated to the new version, thanks for the bug report, check it oooout ;d
Works now, thank you :)
