irt_2pl model still failing

I thought updating the golds in #48 would be enough, but it is still failing. If I recall correctly from the original source of the failures (the Eigen 3.4 PR) it was actually due to a Eigen change which was hardware-specific, so maybe the golds from my machine aren't good enough.

@andrjohns - since you found the issue originally, do you have suggestions on what we should do?