revert unnecessary change

examples/jsm/loaders/STLLoader.js

@@ -76,7 +76,7 @@ STLLoader.prototype = Object.assign( Object.create( Loader.prototype ), {
 		var loader = new FileLoader( scope.manager );
 		loader.setPath( scope.path );
 		loader.setResponseType( 'arraybuffer' );
-		loader.setRequestHeader( scope.requestHeader );
+		loader.setRequestHeader( this.requestHeader );
 
 		if ( scope.crossOrigin === 'use-credentials' ) {