It is 1.5. The end oxygens are equivalent, and distinct from the center oxygen. In drawing the Lewis structure, one could draw a double bond between the center oxygen and one of the ends, and a single bond with the other terminal oxygen; since the terminal oxygens are equivalent, you could flip the order of the bonds. Therefore, you need to take an average of a double and single bond: bond order 1.5.
From Wikipedia: "The structure of ozone, according to experimental evidence from microwave spectroscopy, is bent, with C2v symmetry (similar to the water molecule), O – O distance of 127.2 pm and O – O – O angle of 116.78°. The central atom forms an sp² hybridization with one lone pair. Ozone is a polar molecule with a dipole moment of 0.5337 D. The bonding is single bond on one side and double bond on the other side, and these bonds are blended to become known as resonance structures. The bond order is 1.5 for each side."
This program is horrible for drawing structures: see second link below, about 2/3 the way down the page.
Hope that helped!