update preventing double border line for bordered tables by account for th elements in tr elements

lib/tables.less

@@ -65,6 +65,7 @@ tbody + tbody {
   }
   // Prevent a double border
   thead:first-child tr:first-child th,
+  tbody:first-child tr:first-child th,
   tbody:first-child tr:first-child td {
     border-top: 0;
   }