Fix: add a new GL_OPTIONS to reslove z-fighting problem.

[wangerzi]

I got this Issue and found a problem that I had solved about z-fighting: https://github.com/hujiulong/vue-3d-model/issues/197#issuecomment-653156367

I think we should add this option into DEFAULT_GL_OPTIONS at model-mixin.vue https://github.com/hujiulong/vue-3d-model/blob/e47cbc389de1d5f94985b8ecff0d0137d5fbdd97/src/model-mixin.vue#L41

const DEFAULT_GL_OPTIONS = {
  antialias: true,
  alpha: true,
  logarithmicDepthBuffer: true,
};

reference: https://segmentfault.com/q/1010000014379650/a-1020000021860264 and https://www.cnblogs.com/lst619247/p/9098845.html