1401 and NVIDIA driver 2.8.1

• Updates no longer fail when GitHub's downloads are down. The Mac app now falls back to a copy of each release on nullmothsystems.com when a GitHub download fails, for both driver updates and its own updates. 1401 for Windows does the same for the driver package it puts on the stick. Every file is checked against the release's SHA-256 list and the NullMoth release signature, wherever it came from, and a file that differs by one byte is refused.
• The driver itself is unchanged from 2.8 (same kernel extensions, Metal plugin and Vulkan driver); only its version number moves so the app and the driver keep the same version.