Removing "kine" from irregular inflections

tl;dr: Kine is old, nobody uses it anymore.

Today, I was debugging a mongoid [issue](https://github.com/mongoid/mongoid/issues/3079) and on the issue guy is using a class named Cow. I ran the same example local and couldn't find the collection that the cow was going to, I, of course, was looking for a collection named 'cows' and couldnt find it. After a few minutes of debugging I realize that for activesupport/inflections the plural of cow is kine. Me as a non native english speaker started asking around the office to see if someone would guess the right plural of cow, guess what, nobody said 'kine'. After a [few](http://thebettereditor.wordpress.com/2012/02/10/the-plural-of-cow-is/) [research](http://en.wikipedia.org/wiki/Kine), I saw that kine it is indeed a archaic word. So IMO activesupport should remove that irregular plural.