fix: improve type of TreeNode.children.

Author: mprobst

modules/angular2/src/core/compiler/element_injector.ts

@@ -150,7 +150,7 @@ export class TreeNode<T extends TreeNode<any>> {
   get parent() { return this._parent; }
 
   // TODO(rado): replace with a function call, does too much work for a getter.
-  get children(): TreeNode<any>[] {
+  get children(): T[] {
     var res = [];
     var child = this._head;
     while (child != null) {