I can’t keep straight whether Selena Gomez and Justin Bieber are still an item, but one thing I do know is that on her new album, “Stars Dance,” she has grown up — and not just because she is sporting cleavage inside the glossy CD packaging and muddied up her image in the film “Spring Breakers” earlier this year. Gomez turned 21 on July 22, and is just four years younger than Rihanna, so it makes sense that Gomez is staying away from insipid faux-inspirational songs such as “Who Says” and insipider faux-clever tunes such as “Love You Like a Love Song” of a few years ago. Here, she attempts to emulate Rihanna’s club-ready sound, with more success.. Interestingly enough, the less she tries to be a role model the better she sounds. The album’s opener, “Birthday,”is the best nonsense song about birthdays since The Beatles’ “Birthday,” where they asked us to to dance and take a cha-cha-cha-chance. You could do worse that taking a cha-cha-cha-chance on Gomez’s inoffensive yet mildly fun music and on Nov. 14 at EnergySolutions Arena.