Add missing option for expandable (#8989)

* Add missing option for expandable

Add missing grid option `expandableRowScope` for expandable grid

* Added ng.IScope type for expandableRowScope

ui-grid/ui-grid.d.ts

@@ -1511,6 +1511,10 @@ declare namespace uiGrid {
              * Defaults to 150
              */
             expandableRowHeight?: number;
+            /**
+             * reference to the parent grid scope (the parent scope of the sub-grid element)
+             */
+            expandableRowScope?: ng.IScope | Object;
             /**
              * Mandatory. The template for your expanded row
              */