remove onError callback

examples/webgl_materials_cubemap_mipmaps.html

@@ -40,12 +40,10 @@
 
 					return new Promise( function ( resolve, reject) {
 
-						new THREE.CubeTextureLoader().load( urls,function ( cubeTexture ) {
+						new THREE.CubeTextureLoader().load( urls, function ( cubeTexture ) {
 
 							resolve( cubeTexture );
 
-						}, function ( error ) {
-
 						} );