function inferResponseType (src) {
  var dotLastIndex = src.lastIndexOf('.');
  if (dotLastIndex >= 0) {
    var extension = src.slice(dotLastIndex, src.length);
    if (extension === '.gltf' || extension === '.glb') {
      return 'arraybuffer';
    }
  }
  return 'text';
}
Infer response-type attribute from src.
Default is text(default XMLHttpRequest.responseType)
but we use arraybuffer for .gltf and .glb files
because of THREE.GLTFLoader specification.

@param {string} src
@returns {string}