How to check app running on jailbreak iOS device

Issue #385

From https://github.com/OneSignal/OneSignal-iOS-SDK/blob/master/iOS_SDK/OneSignalSDK/Source/OneSignalJailbreakDetection.m

+ (BOOL)isJailbroken {
    
#if !(TARGET_IPHONE_SIMULATOR)
    
    FILE *file = fopen("/Applications/Cydia.app", "r");
    if (file) {
        fclose(file);
        return YES;
    }
    file = fopen("/Library/MobileSubstrate/MobileSubstrate.dylib", "r");
    if (file) {
        fclose(file);
        return YES;
    }

    file = fopen("/bin/bash", "r");
    if (file) {
        fclose(file);
        return YES;
    }
    file = fopen("/usr/sbin/sshd", "r");
    if (file) {
        fclose(file);
        return YES;
    }
    file = fopen("/etc/apt", "r");
    if (file) {
        fclose(file);
        return YES;
    }
    file = fopen("/usr/bin/ssh", "r");
    if (file) {
        fclose(file);
        return YES;
    }
    
    NSFileManager *fileManager = [NSFileManager defaultManager];
    
    if ([fileManager fileExistsAtPath:@"/Applications/Cydia.app"])
        return YES;
    else if ([fileManager fileExistsAtPath:@"/Library/MobileSubstrate/MobileSubstrate.dylib"])
        return YES;
    else if ([fileManager fileExistsAtPath:@"/bin/bash"])
        return YES;
    else if ([fileManager fileExistsAtPath:@"/usr/sbin/sshd"])
        return YES;
    else if ([fileManager fileExistsAtPath:@"/etc/apt"])
        return YES;
    else if ([fileManager fileExistsAtPath:@"/usr/bin/ssh"])
        return YES;
    
    // Omit logic below since they show warnings in the device log on iOS 9 devices.
    if (NSFoundationVersionNumber > 1144.17) // NSFoundationVersionNumber_iOS_8_4
        return NO;
    
    // Check if the app can access outside of its sandbox
    NSError *error = nil;
    NSString *string = @".";
    [string writeToFile:@"/private/jailbreak.txt" atomically:YES encoding:NSUTF8StringEncoding error:&error];
    if (!error)
        return YES;
    else
        [fileManager removeItemAtPath:@"/private/jailbreak.txt" error:nil];
    
    // Check if the app can open a Cydia's URL scheme
    if ([[UIApplication sharedApplication] canOpenURL:[NSURL URLWithString:@"cydia://package/com.example.package"]])
        return YES;
    
#endif
    
    return NO;
}