Fix appveyor deployments to github releases

[ericwa]

I tried making a tag last week: https://github.com/kduske/TrenchBroom/releases/tag/test-1571

The upload of the Mac and Linux packages from travis worked (using my github credentials in the .travis.yml), the appveyor upload failed though.

Error creating GitHub release: Error reading repository 'kduske/TrenchBroom' releases: 401 - Unauthorized

from: https://ci.appveyor.com/project/kduske/trenchbroom/build/2.0.0-appveyor-164

There's one thing I can try, which is signing in to appveyor with my github account, and regenerate my encrypted github oauth token. I'll make a branch to try that, if it doesn't work, I'll report back here.

[ericwa]

Argh, that didn't do anything.

@kduske if you want to give it a try, here is what to do:

• go to https://github.com/settings/tokens and generate a token with the "public_repo" scope (needs to be kept secret, as this token gives push access to the TB repo)
• go to https://ci.appveyor.com/tools/encrypt and paste in the github oauth token, and press encrypt. Appveyor will return an encrypted token, this can be pasted into appveyor.yml and committed.

[kduske]

@ericwa see PR #1599