Update ng-grid.d.ts

Added pinned to IColumnDef, also wondering why under IGridOptions, data isn't a string, any[] doesn't work in my experience.

ng-grid/ng-grid.d.ts

@@ -176,6 +176,7 @@ declare module ngGrid {
         displayName?: string;
         cellTemplate?: string;
         enableCellEdit?: boolean;
+        pinned?: boolean;
     }
 
     export interface IFilterOptions {