JailBreaking iOS 8.1.3 is currently an impossible task reported by most of the famous jailbreakers .Eventhough you can have a try with 2 different methods .
1) Download and Install iOS 8.2 Beta and Jailbreak.
2) Downgrade the iOS to 8.1.2.
Be careful while trying the 2 options because at any time apple may stop signing to 8.1.2 & 8.2 beta. so confirm it before restoring .