message: Fix color value and unnecessary BOM header
  Color channel values should be separated by commas (standard_surface_copper.mtlx).
  Unnecessary BOM file header (lib/mx_microfacet_diffuse.glsl).
diff: <input name="specular_roughness" type="float" value="0.25" />
  <input name="metalness" type="float" value="1" />
  <input name="coat" type="float" value="1" />
  - <input name="coat_color" type="color3" value="0.96467984 0.37626296 0.25818297" />
  + <input name="coat_color" type="color3" value="0.96467984, 0.37626296, 0.25818297" />
  <input name="coat_roughness" type="float" value="0.20000000298023224" />
  </standard_surface>
  <surfacematerial name="Copper" type="material">
  