Fix packages table css based on linter recommendation

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

ee/app/assets/stylesheets/pages/packages.scss

 .table-holder .packages-table {
   tr {
     th {
-      border-top: none;
+      border-top: 0;
       background: none;
       padding: $gl-padding-top 0;
     }