docs(guide/controller): fix an error in the scope inheritance example

The chained scope creation example at the bottom of this document was using the childCtrl to create the babyScope, instead of the childScope.

Author: JeffreyPalmer

docs/content/guide/dev_guide.mvc.understanding_controller.ngdoc

@@ -268,7 +268,7 @@ describe('state', function() {
         var mainCtrl = $controller(MainCtrl, {$scope: mainScope});
         childScope = mainScope.$new();
         var childCtrl = $controller(ChildCtrl, {$scope: childScope});
-        babyScope = childCtrl.$new();
+        babyScope = childScope.$new();
         var babyCtrl = $controller(BabyCtrl, {$scope: babyScope});
     }));