If you check out the Skaven FAQ, they've changed it to:How many ranks do they attack in? Is it still two or do they get to attack in three due to the new rules?
So, essentially they always fight in 3 ranks to the front now.Page 54 – Wave of Rats
Change the second and third sentence to “Giant Rats have the
Fight in Extra Ranks special rule, except that they fight with an
extra rank even in the turn they charge.