Operating system: Apple os
Graphics card: iris pro 1536
Blender Version 280 b3f96da2e605
Broken: (example: 2.80, edbf15d3c044, master, 2018-11-28, as found on the splash screen)
Short description of error
doesn't export gltf alpha properly, which in previous version (280 a9da750aee08) used to work just fine)
Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).