move transition into `example-enter-active` selector

I was only able to get these animations to work by placing the `transition` declaration within the `example-enter-active` selector. When it was in the `example-enter` selector it didn't work. 

For whatever reason the animation began when the `example-enter` classname was added and was then halted when the `example-enter-active` classname was added. 

Chrome Version 36.0.1985.143