Updated to KSP-AVC Plugin 1.1.3 or later.

Tyrope's KSP-AVC Utility is now defunct, and doesn't need to be supported; only cybutek's KSP-AVC Plugin will be supported going forward.

So long as we use GitHub release tags that include the version number in them, we don't need to worry about race conditions between updating the online `.version` file and actually publishing the release; the version inferred from the latest release tag will override the version in the `.version` file. Same goes for the download location; we needn't update it manually.

EDIT: clarified wording based on pjf's post