Fix the documentation issue about cacheSerializer

@@ -220,7 +220,7 @@ SDWebImageManager.sharedManager.cacheKeyFilter = ^(NSURL * _Nullable url) {
  * @note The `image` arg is nonnull, but when you also provide a image transformer and the image is transformed, the `data` arg may be nil, take attention to this case.
  * @note This method is called from a global queue in order to not to block the main thread.
  * @code
- SDWebImageManager.sharedManager.cacheKeyFilter = ^NSData * _Nullable(UIImage * _Nonnull image, NSData * _Nullable data, NSURL * _Nullable imageURL) {
+ SDWebImageManager.sharedManager.cacheSerializer = ^NSData * _Nullable(UIImage * _Nonnull image, NSData * _Nullable data, NSURL * _Nullable imageURL) {
     SDImageFormat format = [NSData sd_imageFormatForImageData:data];
     switch (format) {
         case SDImageFormatWebP: