GLTFExporter: Replace QUESTION with TODO

examples/js/exporters/GLTFExporter.js

@@ -448,7 +448,7 @@ THREE.GLTFExporter.prototype = {
 		 */
 		function processImage( map ) {
 
-			// @QUESTION Needs image cache for the case where two different textures share the same image?
+			// @TODO Cache
 
 			if ( ! outputJSON.images ) {