KHR_materials_common samples for glTF2.0 need update

[donmccurdy]

Several models have the diffuse textures in an array:

"KHR_materials_common": {
    ...
    "values": {
        ...
        "diffuse": [
            0
        ],
        ...

From KhronosGroup/glTF#965, I assume that should be diffuseTexture: 0.

transparency and shininess are arrays, and should presumably be floats:

"shininess": [
    50.0
],
"transparency": [
    1.0
]