Fix documenting of the 'Tab/onAnimateOutEnd' private property

Author: AlexKVal

src/Tab.js

@@ -9,6 +9,10 @@ const Tab = React.createClass({
      */
     active:          React.PropTypes.bool,
     animation:       React.PropTypes.bool,
+    /**
+     * It is used by 'Tabs' - parent component
+     * @private
+     */
     onAnimateOutEnd: React.PropTypes.func,
     disabled:        React.PropTypes.bool,
     title:           React.PropTypes.node