Docs: correct gif resize example

lib/output.js

@@ -521,13 +521,9 @@ function webp (options) {
  *   .toFile('animated.gif');
  *
  * @example
- * // Create 128x128, non-dithered thumbnail of an animated GIF
- * const { pages } = await sharp('animated.gif').metadata();
- * const gif = await sharp('animated.gif', { animated: true })
- *   .resize({
- *     width: 128,
- *     height: 128 * pages
- *   })
+ * // Create a 128x128, cropped, non-dithered, animated thumbnail of an animated GIF
+ * const out = await sharp('in.gif', { animated: true })
+ *   .resize({ width: 128, height: 128 })
  *   .gif({ dither: 0 })
  *   .toBuffer();
  *