Fix a build error when compiling on macOS Make `AVCaptureSessionPreset1280x720` as the default value of sessionPreset.
Fix a build error when compiling on macOS
Make `AVCaptureSessionPreset1280x720` as the default value of
sessionPreset.

rkpant/ZXingObjC,peacemoon/ZXingObjC,TheLevelUp/ZXingObjC,rkpant/ZXingObjC,peacemoon/ZXingObjC,trsathya/ZXingObjC,benjohnde/ZXingObjC,trsathya/ZXingObjC,TheLevelUp/ZXingObjC,benjohnde/ZXingObjC