message: Fix bad skybox color in web demo.
  In a previous CL today, I changed the skybox to RGBM but forgot to
  change the format. Thanks Romain for catching this.
diff: @@ -215,7 +215,7 @@ SkyLight getSkyLight(Engine& engine, const char* name) {
  .width(size)
  .height(size)
  .levels(1)
  - .format(Texture::InternalFormat::RGBA8)
  + .format(Texture::InternalFormat::RGBM)
  .sampler(Texture::Sampler::SAMPLER_CUBEMAP)
  .build(engine);
  {
  