assign background to row of .table-striped

if background is not set on row, striping doesn't work properly in responsive tables where row and cells are set to  display: block.

less/tables.less

@@ -106,6 +106,7 @@ th {
 
 .table-striped {
   > tbody > tr:nth-child(odd) {
+    background-color: @table-bg-accent;
     > td,
     > th {
       background-color: @table-bg-accent;