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I'd suggest 2x AEther Vial and 3x Cavern of Souls to make your goblins uncounterable. The 2x Fervor just seems like overkill with 4 chieftains. I'd replace those with the vials. I played against a goblin deck at GP Lincoln and it used the vials to essentially flash in chieftains on the end step. It was a pain to deal with.
Also, since Goblin War Strike isn't legal in modern, how about 4x Goblin Bushwhacker instead? They give the same effects as both the Goblin Wardriver and Fervor combined, and they give all your tokens haste.
Hope this helps. Good luck!
Goblin King is modern legal, but not Warchief.