In Georgia, the credibility of a witness is to be determined by the jury, and the credibility of a victim may not be bolstered by the testimony of another witness. Thus, a witness may not give an opinion as to whether the victim is telling the truth." Stillwell v. State, 294 Ga. App. 805, 806-807 (2) (a) (670 SE2d 452) (2008). Improper bolstering occurs when a witness gives an opinion as to whether another witness is telling the truth. Chauncey v. State, 283 Ga. App. 217, 220 (3) (641 SE2d 229) (2007).