allowsBackgroundLocationUpdates on iOS 8.4

[flames85]

_locationManager.allowsBackgroundLocationUpdates = YES; will crash on ios8.4.
so I modify to
if([_locationManager respondsToSelector:@selector(setAllowsBackgroundLocationUpdates:)]) {
// We now have iOS9 and the right capabilities to set this:
[_locationManager setAllowsBackgroundLocationUpdates:YES];
}

[liuyan3176]

Thanks a lot~