Inconsistent item margin

[kirsty-hames]

The current item margin is applied to all items except the :last-child. This is fine for the default stacked item layout however all items set with _columns layout should have margin applied to all items equally.

I'd suggest removing the generic margin style on line 135:

.list-item:not(:last-child) {
   margin-bottom: @item-margin * 2;
}

In favour of:

.list__container.has-columns .list-item,
.list__container:not(.has-columns) .list-item:not(:last-child) {
  margin-bottom: @item-margin * 2;
}