Update 10.1-animation.md

Changed "if" to "even when" for clarity.

docs/10.1-animation.md

@@ -54,7 +54,7 @@ var TodoList = React.createClass({
 ```
 > Note:
 >
-> You must provide [the `key` attribute](/react/docs/multiple-components.html#dynamic-children) for all children of `ReactCSSTransitionGroup`, even if rendering a single item. This is how React will determine which children have entered, left, or stayed.
+> You must provide [the `key` attribute](/react/docs/multiple-components.html#dynamic-children) for all children of `ReactCSSTransitionGroup`, even when only rendering a single item. This is how React will determine which children have entered, left, or stayed.
 
 In this component, when a new item is added to `ReactCSSTransitionGroup` it will get the `example-enter` CSS class and the `example-enter-active` CSS class added in the next tick. This is a convention based on the `transitionName` prop.