bug in irr

[stevenjwolfman]

This program yields the wrong solution

irb(main):080:0> [-100,1,50,50,50].irr
-1.802970927840458773306399728082340970593857587447338725049180655651412701292513248441308155402999109362230823362680689447524157318592267102196347382451152920776482908594822377770535664250863```

[weshatheleopard]

I believe PR #39 has the fix, but the maintainer disappeared again.