There’s no way to spoil the ending of “Book Club,” the chick-of-a-certain-age flick starring Jane Fonda, Candice Bergen, Diane Keaton and Mary Steenburgen as members of a book club that’s met monthly for 40 years. It’s the same as every fairy tale: happily, ever after.Representing the opposite end of the horological spectrum from the Disney princesses, the “Book Club” women want the same thing that every heroine has wanted since Cinderella first picked up her broom — to be …