Not Updated For Current Season
The masteries shown here are not yet updated for the current season, the guide author needs to set up the new masteries. As such, they will be different than the masteries you see in-game.
My own way of building Jax after his slight rework. He is still weak early game, but after completing your Guinsoo's and hitting level 6 you should be able to jungle for Red and blue buffs and start ganking. I leave one extra item slot for your choice of Lich Bane or Trinity Force. Whichever you want.