In the U.S., the verb shrivel is inflected shriveled and shriveling. Outside the U.S., the older forms, shrivelled and shrivelling are still standard.
The American forms are well-established, having gained prevalence in the middle of the 20th century. As with many of these l-ending verbs, the more traditional forms continue to appear regularly in the U.S., even if only a fraction of the time. The more American forms, meanwhile, have not made their way outside the U.S.