Merge pull request facebook#2581 from spicyj/rm-elt-docs

Update variable name and doc type to be accurate

src/browser/ui/ReactMount.js

@@ -267,16 +267,16 @@ var ReactMount = {
   /**
    * Take a component that's already mounted into the DOM and replace its props
    * @param {ReactComponent} prevComponent component instance already in the DOM
-   * @param {ReactComponent} nextComponent component instance to render
+   * @param {ReactElement} nextElement component instance to render
    * @param {DOMElement} container container to render into
    * @param {?function} callback function triggered on completion
    */
   _updateRootComponent: function(
       prevComponent,
-      nextComponent,
+      nextElement,
       container,
       callback) {
-    var nextProps = nextComponent.props;
+    var nextProps = nextElement.props;
     ReactMount.scrollMonitor(container, function() {
       prevComponent.replaceProps(nextProps, callback);
     });