[minor] tree grid expand collapse button visible

frappe/public/css/tree_grid.css

@@ -10,12 +10,13 @@
 	height: 9px;
 	width: 9px;
 	display: inline-block;
+	visibility: visible;
 }
 
 .toggle.expand {
-	background: url("../frappe/js/lib/slickgrid/images/expand.gif") no-repeat center center;
+	background: url("/assets/frappe/js/lib/slickgrid/images/expand.gif") no-repeat center center;
 }
 
 .toggle.collapse {
-	background: url("../frappe/js/lib/slickgrid/images/collapse.gif") no-repeat center center;
+	background: url("/assets/frappe/js/lib/slickgrid/images/collapse.gif") no-repeat center center;
 }