fix(grid): fix grid nested data bind dropdown padding

Author: Hristo313

src/app/grid/grid-nested-data-binding/grid-nested-data-bind.scss

@@ -30,7 +30,7 @@ igx-input-group {
 
 ::ng-deep {
     .expand {
-        padding: 2px;
+        padding: 0;
         background: transparent;
         &:hover {
             background: transparent;