Appveyor should support pre-releases

[lu-zero]

here an example of the problem.

[EwoutH]

It's maybe this problem: https://help.appveyor.com/discussions/problems/13622-error-creating-github-release-not-found

In attempts to fix the error, I've changed permissions in access token to following:
notifications, public_repo, repo:status, repo_deployment

The token can be edited on https://github.com/settings/tokens