Add 4th array element to baseColorFactor to match specification
See https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#metallic-roughness-material
4th parameter is for base opacity and is expected by e.g. three.js
See https://github.com/KhronosGroup/glTF/tree/master/specification/2.0#metallic-roughness-material
4th parameter is for base opacity and is expected by e.g. three.js