You Cannot Jailbreak iOS 8.4.1
If you want to jailbreak your iPhone 6, do not download the iOS 8.4.1 update.
There is no iOS 8.4.1 jailbreak. Apple plugged up the exploits used by the iOS 8.4 update and now developers have to go back to the drawing board.
We doubt that we'll see an iOS 8.4.1 jailbreak released this close to the iOS 9 update so you might have to wait several more weeks to see another working jailbreak emerge.