Update _notifications.less

Author: VladimirZaets

app/design/adminhtml/Magento/backend/Magento_Backend/web/css/source/module/header/actions-group/_notifications.less

@@ -103,7 +103,8 @@
         padding: .3em .5em;
         position: absolute;
         top: 50%;
-        width: 18px;
+        min-width: 18px;
+        height: 18px;
     }
 }