Correct the CSS example for 'appear' transition

Move transition from `.example-appear` to `.example-appear.example-appear-active`

docs/10.1-animation.md

@@ -101,11 +101,11 @@ During the initial mount `ReactCSSTransitionGroup` will get the `example-appear`
 ```css
 .example-appear {
   opacity: 0.01;
-  transition: opacity .5s ease-in;
 }
 
 .example-appear.example-appear-active {
   opacity: 1;
+  transition: opacity .5s ease-in;
 }
 ```